Introduction

International counterterrorism law (CTL) frequently applies to conduct in armed conflict regulated by international humanitarian law (IHL). Depending on one's perspective, this brings advantages or disadvantages. On the one hand, CTL can play a valuable role in complementing IHL in the suppression of undesirable violence, while avoiding the political difficulties of amending IHL itself. On the other hand, the co-application of CTL has the potential to conflict with long-standing and sometimes sensitive IHL rules or undermine IHL policy interests.

Neither CTL nor IHL purports to be lex specialis or self-contained at the regime level so as to wholly exclude the other; CTL applies in armed conflict just as do international human rights law, international criminal law, international environmental law and so on. Nor does CTL clearly, explicitly and uniformly spell out the legal relationships where specific rules of the two branches interact. Rather, some international counter-terrorism conventions (ICTCs)Footnote ¹ since 1963 exclude certain conduct, actors or targets in armed conflict from their scope, while otherwise co-applying with IHL. Other ICTCs are silent on the relationship but raise potential conflicts with IHL. So too does decentralized national implementation of binding United Nations (UN) Security Council counterterrorism resolutions since 2001, some of which vaguely affirm that national CTL measures must comply with IHL but do not identify all specific relevant IHL rules which must be respected.

This article aims to clarify the conceptual, policy and interpretive debatesFootnote ² about the interaction of CTL and IHL. It considers firstly the potential advantages of co-applying CTL, and secondly the key disadvantages of CTL intruding on IHL's domain. Whether the interests of each regime can be adequately accommodated through co-application largely depends on the scope of particular CTL and IHL rules, including the existence and extent of any CTL provisions deferring to IHL. The subsequent part of the article accordingly explores how IHL is diversely addressed in the ICTCs (from implicit and explicit partial exclusions to silence). This is followed by consideration of the Security Council's limited, albeit growing, attention to IHL, and the potentially adverse impacts on IHL of national implementation of CTL measures.

The issues discussed in this article are pressing not only because the UN General Assembly's Draft Convention for the Prevention and Suppression of International Terrorism (Draft UN Convention), formally under negotiation since 1999, is still struggling to demarcate its approach to IHL, but also because (by virtue of Security Council CTL obligations) all States are already required to suppress terrorist acts – in the absence of a universal definition of them or any agreed approach to their interaction with IHL. Even if a State is not involved in armed conflict (as most States are not), it must still cooperate in the prevention and suppression of terrorism affecting another State. States can thus be required to assist foreign States in suppressing non-State organized armed groups (OAGs) in non-international armed conflict (NIAC), including by criminalizing insurgent fighting in foreign civil wars and removing the “political offence exception” to extradition. CTL and IHL may co-apply in many contemporary conflicts, including Afghanistan, Colombia, Iraq, Mali, Nigeria, Palestine, Somalia, Syria and Yemen,Footnote ³ as well as in relation to “foreign fighters” from other States. These developments have not only produced legal incoherence – due to the divergence in national approaches – but also discourage compliance with IHL by OAGs, undermine prospects for peace and reconciliation, and may displace accountability for war crimes – and justice for victims – through an emphasis on prosecuting less grave national terrorism offences.

The article concludes by proposing the optimal approach to the CTL–IHL interface, reconciling IHL and counterterrorism imperatives as far as possible and minimizing one field playing “trumps” at the expense of the other. It makes two concrete suggestions. Firstly, the Draft UN Convention, Security Council resolutions, and regional and national laws should exempt from CTL all activities of armed forces during armed conflict which are not unlawful under IHL, following the “best practice” approach in Canadian and New Zealand law. Secondly, the Security Council should require all of its CTL measures to be implemented in conformity with relevant, specific IHL rules, including on medical and humanitarian activities.

Advantages of co-application

It is well known that much terrorist conduct – namely, violence against civilians designed to intimidate a population or compel a governmentFootnote ⁴ – is already addressed by IHL. This foremost includes the numerous IHL rules (some of which entail criminal responsibility) prohibiting deliberate, indiscriminate or disproportionate attacks on civilians and civilian objects (including medical and humanitarian relief personnel, transports and objects, as well as cultural property and religious places), hostage-taking, perfidy, the use of certain weapons, and reprisals against civilians. In addition, there are specific IHL prohibitions on terrorism (and the related war crime of intending to spread terror amongst civilians). An overarching policy question is whether these are enough to suppress terrorist-type violence in armed conflict, or whether CTL adds different and valuable tools. A number of potential contributions of CTL may be identified from a counterterrorism standpoint.Footnote ⁵

First, CTL substantively criminalizes certain undesirable conduct which is not prohibited by IHL. Numerous examples may briefly be given, though most are highly specialized and are not common in armed conflicts. For example, IHL does not address the nuclear material offences of embezzling or fraudulently obtaining nuclear material, demanding nuclear material by force or intimidation, unlawfully dealing with nuclear material, or nuclear smuggling;Footnote ⁶ nor does it address the nuclear terrorism offences of unlawful possession of radioactive material, or making a radioactive device, with intent to harm.Footnote ⁷ Further, there are no comparable IHL prohibitions or war crimes in relation to various aviation and maritime safety offences, such as communicating false information and thereby endangering aircraft safety,Footnote ⁸ or unlawfully transporting explosives or biological, chemical or nuclear weaponsFootnote ⁹ (although weapons treaties more narrowly prohibit and criminalize the “transfer” of some of these weaponsFootnote ¹⁰).

As regards more general terrorism offences, the Draft UN Convention would criminalize attacks on communication systems which are likely to result in major economic loss, but under IHL, if civilian data is not an “object” which can be kinetically “attacked”,Footnote ¹¹ IHL does not prohibit attacks upon it, let alone criminalize them. More controversially, national CTL offences may criminalize civilian direct participation in hostilities (DPH) (whether by members of OAGs performing a continuous combat function (CCF), or more sporadic participation), for instance by resort to offences such as membership of a terrorist organization or foreign fighter offences. In international armed conflict (IAC), such persons are simply not entitled to the combatant's immunity from national criminal prosecution for hostile acts that are in conformity with IHL. Further, in both IAC and NIAC such persons may be targeted for the duration of their participation, detained on security grounds, and prosecuted for any national offences (including terrorism) as well as for any consequential harm constituting war crimes (such as perfidy or physical injury).

Secondly, CTL may criminalize conduct which is prohibited under IHL but not a war crime. For example, a failure to take adequate precautions in targeting is not a war crime in any conflict, whereas national terrorism offences may make it an offence to recklessly endanger life or the public, thus enhancing civilian protection. In NIAC – at least under the Rome Statute of the International Criminal Court (ICC) – there is also no crime of launching an attack on civilian objects (as opposed to persons), an indiscriminate attack, an attack which would cause disproportionate civilian casualties, illegal detention, or using human shields. CTL may criminalize these. CTL may also criminalize attacks on the environment,Footnote ¹² whereas IHL only does so in IAC and then only under the Rome Statute and if very high thresholds are met.Footnote ¹³ Even where such conduct already constitutes ordinary national crimes, CTL liability can enable wider international cooperation and bring additional investigative tools.

Thirdly, where CTL and war crimes apply to the same conduct, elements of CTL offences may be more specific. Examples include the CTL offences of aircraft hijackingFootnote ¹⁴ and emplacing a bomb on an aircraft,Footnote ¹⁵ compared with the more general IHL rules against attacking or attempting to attack a civilian object or hostage-taking. CTL can thus expand the armoury of charges available and more accurately reflect what is precisely wrongful about an act.

Fourthly, CTL often criminalizes early preparatory conduct which is not covered by war crimes or IHL prohibitions. On the one hand, the extended modes of criminal responsibility under the ICTCsFootnote ¹⁶ and IHLFootnote ¹⁷ are not dissimilar. But in implementing UN Security Council Resolution 1373, many States have enacted more precautionary offences which criminalize preparatory conduct well before criminal intent has crystallized into an attempt, or conduct where a person acts alone and there is thus no (group) conspiracy prior to the attempt. Such offences include the mere possession of a weapon, explosive, vehicle, document or object which could be used in a future attack, before any overt act is initiated. They also include offences of providing or receiving terrorist training (for instance, on weapons, tactics or targets) and inciting, advocating, praising or glorifying terrorism (including to radicalize or recruit others). There are also numerous offences relating to various forms of support to terrorist organizations, such as acts of finance, recruitment, membership, association, support or training.

In contrast, IHL does not prohibit groups from, or criminalize their members for, direct or indirect participation in hostilities, but focuses on unlawfully harmful conduct (such as wilful killing or perfidy). It also limits modes of liability to more traditional ones whereby an act must bear a more proximate relationship to the eventual commission of a crime in order to attract criminal liability. For instance, whereas financing a specific attack on civilians could constitute the accessorial offence of aiding and abetting a war crime, the stand-alone, principal CTL offence of giving funds to a person involved in terrorism or a terrorist organization – for purposes other than a contemplated terrorist act – would not constitute complicity in a war crime.

Even where a terrorist act is also a war crime, prosecution for a terrorism offence may be tactically easier and more fruitful for law enforcement, particularly for group-based offences with low bars of membership, association, or indirect or peripheral support for the group, proved by self-incriminating social media records. It may avoid the technical complexities, security challenges and resource burdens (particularly in weak, fragile or developing States affected by conflict) of forensically collecting battlefield evidence of war crimes in remote, dangerous conflict zones, while still achieving the criminological goal of incapacitating the offender through equally lengthy (if not lengthier) terms of imprisonment for terrorism offences. In Europe and the United States, for example, most prosecutions of returning “terrorist fighters”, or foreign immigrant fighters, from Syria and Iraq have involved either terrorist or ordinary criminal offences, not international crimes.Footnote ¹⁸ As discussed below, however, some support or organization-based offences may conflict with IHL guarantees for medical and humanitarian personnel and their activities, while some have also raised international human rights law issues, such as by infringing on the principle of legality.Footnote ¹⁹

Fifthly, CTL imposes distinctive obligations on States concerning jurisdiction and cooperation. On the one hand, all war crimes (in IAC or NIAC) are subject to a right of universal jurisdiction under customary IHL, and an implied duty under the Geneva Conventions of 1949 to establish such jurisdiction over “grave breaches” in IACFootnote ²⁰ (but there is no treaty or customary law duty to establish universal jurisdiction over war crimes in NIAC). The jurisdictional picture is similarly both fragmented yet fairly extensive for terrorism offences. The ICTCs specify various grounds of jurisdiction (such as territoriality and nationality) but also residually require a State to establish quasi-universal jurisdiction where a (non-national) suspect who has committed an offence abroad is present in the State's territory.Footnote ²¹ Such jurisdiction is more limited than under the Geneva Conventions, which do not require the presence of an offender,Footnote ²² but more expansive in that jurisdiction must be established over offences, including in NIAC (unlike in IHL, which confers a customary right but imposes no duty).

Some specific CTL offences under Security Council resolutions are, however, subject only to territoriality or nationality jurisdiction (as for certain financing and foreign terrorist fighter offences,Footnote ²³ and this also implicitly the position for more extensive suite of general CTL offences in paragraph 2(e) of Resolution 1373.Footnote ²⁴ In practice, jurisdictional grounds in disparate national laws are often limited rather than asserting universal jurisdiction, thereby reducing the potential for accountability (although national war crimes jurisdiction can be similarly limited in practice).

Another difference between IHL and CTL concerns the exercise of jurisdiction and cooperation. Only “grave breaches” in IAC are subject to a treaty duty to investigate offences, “extradite or prosecute” and provide mutual legal assistance, but not other violations of the laws and customs of war (in IAC or NIAC) or violations of Article 3 common to the Geneva Conventions in NIAC. In contrast, States must extradite or prosecute, and provide mutual assistance, in relation to all ICTC offences, as well as in relation to all terrorist acts (including preparatory offences) under Resolution 1373.Footnote ²⁵ Such obligations of transnational cooperation are essential to combating impunity where fugitives cross borders. However, there is arguably a customary IHL duty to investigate, “prosecute or extradite”, and cooperate (including mutual assistance in investigations, arrests and prosecutions, and through extradition).Footnote ²⁶

Sixthly, CTL imposes its own specific duties to prevent offences which differ from those in IHL, although IHL contains its own preventive measures covering some of the same ground. Under the ICTCs, States must take all practicable measures to prevent, and counter preparations in their territories for, the commission of offences within or outside their territories, including “measures to prohibit in their territories illegal activities of persons, groups and organizations that encourage, instigate, organize or engage in the perpetration of” offences.Footnote ²⁷ In addition, States must cooperate by exchanging information and coordinating administrative and other measures to prevent offences,Footnote ²⁸ including those prepared abroad and directed against other States. Detailed preventive obligations are also set out in Resolution 1373Footnote ²⁹ and in other resolutions on preventing related threats such as foreign fighters. A national and inter-State machinery of prevention is thus in motion to address terrorist offences.

IHL's measures of prevention are both narrower and more comprehensive than CTL's. Many are limited to a party's own conduct (unlike CTL), for instance through measures to execute obligations; orders and instructions; repression of breaches; command responsibility; commanders’ duties; dissemination; and legal advisers.Footnote ³⁰ More generally, the national criminalization of war crimes – like terrorist offences – aims to deter and thus prevent crimes by any person. The obligation in Article 1 common to the Geneva Conventions to “ensure respect” for IHL requires a duty not only to stop violations but also “to prevent violations where there is a foreseeable risk that they will be committed and to prevent further violations in case they have already occurred”.Footnote ³¹ It applies not only to a party's own forces but also to populations under its control;Footnote ³² in this respect it covers similar ground to the CTL measures targeting terrorist preparations in the State's territory. Common Article 1 arguably also extends to the ensuring of respect by other parties to a conflict,Footnote ³³ in which case it partly coincides with the CTL duty to exchange information and coordinate measures where, for instance, a State suspects that a crime is being prepared abroad against another State.

Seventhly, CTL may entail stronger or special investigative or other law enforcement powers compared with IHL. The presumed extraordinary menace of terrorism is frequently invoked to justify exceptional powers for police and intelligence agencies in relation to surveillance; stop, search and seizure; preventive freezing and confiscation of assets; lesser judicial controls (such as warrants); extended periods of pre-charge detention; modifications to bail procedures; preventive security detention; restrictive “control orders”; or lower standards of proof. At trial, suspects may face modified procedures to accommodate security concerns, such as closure of courts or limited disclosure of classified information. Upon conviction, terrorists may receive unusually lengthy sentences of imprisonment due to sentencing policies. All of this may make CTL more attractive than IHL as a way of dealing with offenders, assuming such laws and procedures are consistent with human rights law. Violations of human rights may undermine accountability for terrorism if, for example, evidence is tainted or trials are unfair.

Finally, there may be an important expressive dimension to labelling conduct as terrorist rather than as a (mere) IHL violation or even a war crime. The term “terrorism” has a powerful stigmatizing and denunciatory effect of its own. It conjures up a particular kind of grave criminality – not necessarily worse than a war crime, but reflecting different injured interests that justify distinctive suppression. The UN General Assembly and Security Council have routinely condemned terrorism as a threat to international security, human rights and stable governanceFootnote ³⁴ (interests which war crimes can also threaten). They have frequently condemned terrorist acts by OAGs in armed conflict (whether in NIAC or IAC involving occupation), for example in Afghanistan, Iraq, Syria, Nigeria, Mali, Yemen and Israel/Palestine. They have sometimes called for the prosecution of those involved in terrorist acts in conflicts,Footnote ³⁵ albeit without indicating which acts should be prosecuted specifically as terrorism, international crimes or ordinary crimes. While States are not required (either by most of the ICTCs or by Security Council resolutions) to explicitly qualify terrorist acts as specifically terrorist offences in national lawFootnote ³⁶ (the same is strictly true of war crimes under IHLFootnote ³⁷), this is the predominant approach.

Separately, one pragmatic reason for pursuing terrorism charges is that some States simply lack relevant war crimes legislation. In Syria, for example, there is no such law applicable to NIACs;Footnote ³⁸ Afghanistan only implemented international crimes into domestic law in 2018;Footnote ³⁹ and proposed international crimes laws in Iraq (including the Kurdistan Region) and Nigeria are yet to be adopted (as of mid-2021). In these States, terrorism prosecutions have predominated by default (including prosecutions by some OAGsFootnote ⁴⁰). Other States, meanwhile, lack both CTL and war crimes offences. Somalia has relied on military law offences and courts (as well as detention, disarmament, demobilization and reintegration) to deal with Al-Shabaab;Footnote ⁴¹ a CTL bill endorsed by the cabinet in 2013 is yet to be passed, after its sponsor was killed in the conflict, and there is no bill at all on international crimes.

Disadvantages of co-application

What are the disadvantages of the co-application of CTL? There are legal and policy considerations. Firstly, where CTL and war crimes prohibit the same conduct, CTL may seem unobjectionable because it simply reinforces IHL, as where both criminalize attacks on civilians. Even in this best case, however, war crimes may be a preferable paradigm precisely because they are crimes under customary international law. They are universally and well defined,Footnote ⁴² and much longer and more firmly established, than newer, more divergent national terrorism offences (particularly those arising from Security Council standards which do not define terrorist acts, and which often raise human rights concerns). Labelling conduct as a war crime has a unique denunciatory power of its own – it is more universal and less political than terrorism, and widely understood as entailing the gravest international criminality. Certainly where a war crime has an element additional to an terrorist offence, and there is sufficient evidence to prosecute, it should be prosecuted as a war crime in order to recognize the full nature and scope of the criminality involved and to do justice to victims of international crimes.Footnote ⁴³ Where the elements of crimes differ, attention should be given to cumulative charging.

Further, war crimes attract universal jurisdiction, unlike the possibly more limited extraterritorial ambit of some States’ terrorism offences implementing Security Council resolutions (in contrast to ICTC offences, which require quasi-universal jurisdiction). There are long-established modalities of cooperation (such as extradition and mutual assistance) between many States in relation to war crimes. There is also a rich body of international jurisprudence on war crimes,Footnote ⁴⁴ unlike the much more jurisdiction-specific case law and parochial national and regional practices on terrorism. Unlike terrorism, allegations of war crimes also potentially engage international jurisdiction (of the ICC),Footnote ⁴⁵ special IHL mechanisms (such as the International Fact-Finding Commission) and international human rights mechanisms (such as commissions of inquiry) with a mandate to investigate IHL or international criminal law violations (but not normally “terrorism” offences).

Secondly, IHL was developed as a (largely) self-contained regime based on the best attainable (albeit not necessarily the best) compromises between military necessity and humanitarian protection. Interposing extraneous bodies of law, without due regard for the carefully negotiated balancing within IHL, has the potential to undermine the essential interests of the belligerents and thus compliance with IHL (including protection of civilians and fighters alike).

For example, CTL would directly collide with IHL if it criminalized lawful attacks by State forces in IAC, overriding combatant immunity. Likewise, there would be a conflict if CTL offences such as terrorist financing or providing “support” criminalized or impeded the impartial provision of medical or humanitarian relief.Footnote ⁴⁶ If CTL offences prime facie apply to such conduct, some means is needed to resolve the conflict, whether through (1) harmonious interpretation of the two rules, (2) regarding one rule as lex specialis to “trump” the other, (3) incorporating an exception into the CTL norm, or (4) relying on informal means such as prosecutorial discretion (an undesirable optionFootnote ⁴⁷). These techniques are considered below.

Indirect or implicit conflicts are more difficult: to use earlier examples, do CTL offences interfere in IHL if IHL deliberately chooses – for reasons of military exigency or otherwise – not to criminalize attacks on the environment, or a failure to take precautions, in IAC; or to prohibit, but not criminalize, indiscriminate or disproportionate attacks in NIAC; or not to prohibit or criminalize direct participation in hostilities in NIAC? Such acts may be criminal under CTL in NIAC, or even in IAC to the extent that combatant immunity only covers acts that are lawful under IHL, not war crimes or other violations of IHL prohibitions Footnote ⁴⁸ (such as the failure to take precautions, or attacking the environment).

Thirdly then, even where there is no direct, formal legal conflict between CTL and IHL rules, CTL measures may undermine policy interests inherent in IHL. The risk is particularly acute in the following area. IHL neither authorizes nor prohibits civilian DPH (including CCF by members of OAGs), but regulates its consequences. CTL may, however, criminalize such conduct regardless of whether it otherwise complies with IHL on the conduct of hostilities, as where OAGs attack only military objectives, avoid excessive civilian casualties, and use lawful means and methods of war. Such CTL offences cannot technically conflict with IHL, since the conduct is not authorized under IHL. To the contrary, IHL permits States Parties to criminalize civilian DPH, for instance under the occupier's security laws in occupied territory;Footnote ⁴⁹ while national law may criminalize it in a State's own territory in IAC or NIAC.

At most, IHL encourages States to confer the widest possible amnesty at the end of a NIAC (under Additional Protocol II (AP II) only, not also under common Article 3) for acts which did not violate IHL.Footnote ⁵⁰ In this sense, the incentives for OAGs to comply with IHL have always been very limited, resulting from States’ concerns to protect their sovereign right to restore law and order in their territories.

The question, then, is not whether such conduct cannot be criminalized at all, so much as whether it is appropriate to transnationally criminalize it as terrorism – that is, to establish extraterritorial criminal jurisdiction over such conduct in a foreign State's territory, and to either prosecute fugitive offenders or extradite them back to the territory of the conflict. There is certainly no general international law rule prohibiting this, as long as the definition of terrorist offences complies with international human rights law, for instance as regards the principle of legality (precision and foreseeability in offences) or of non-discrimination. Moreover, on numerous occasions the Security Council and General Assembly (and through them, States collectively) have clearly depicted certain OAGs in armed conflicts as terrorist – such as Al-Qaeda, the so-called Islamic State (IS), Al-Nusra and Boko Haram – because of the nature of the acts committed by their members. Such identification has not only been for the purpose of imposing sanctions but also to encourage States to bring to justice the perpetrators. Both Security Council resolutions addressing terrorism and the ICTCs thus envisage at least some co-application of CTL and IHL.

A number of policy counter-arguments may nonetheless be made. The International Committee of the Red Cross (ICRC) warns precisely against criminalizing “any act of violence” by an OAG as unlawful terrorism when it is not unlawful under IHL, since doing so “is likely to diminish any incentive to comply with IHL”.Footnote ⁵¹ It makes a similar point in relation to labelling groups as terrorist (which often triggers the criminal liability of members), since this too “carries the risk that the OAG loses an incentive to abide by that body of law”, particularly the duty to distinguish between civilians and military objectives.Footnote ⁵² Clearly, if one will be criminalized as a terrorist – whether because of one's conduct, or for membership or support of a terrorist group – regardless of whether one respects IHL, the perceived advantages of complying with IHL may be reduced.

The ICRC's claims are intuitive and common-sense, rather than being empirically substantiated by whether the application of CTL does, in fact, push OAGs to be less IHL-compliant, but they are nonetheless grounded in the ICRC's operational experience in conflicts. This is not to say that labelling individuals or groups as terrorist decimates all incentives to comply, since there are many other reasons why groups in particular may still wish to comply: their moral identity or religious values; appealing to civilian hearts and minds; gaining support from diasporas or foreign State sponsors; political legitimacy; facilitating humanitarian relief to “their” people; demonstrating that they are not war criminals, unlike State forces; or to show that they are not, in truth, terrorists.Footnote ⁵³ This is also not to say that all OAGs are amenable to IHL socialization or responsive to its faint incentives for compliance. Violating IHL is the mission or core business of some “terrorist” groups (such as IS, Al-Qaeda, Boko Haram and Abu Sayyaf), which are not deterred by war crimes law, let alone the nuance that IHL does them the favour of neither prohibiting nor authorizing combat, and leaves the issue of whether they are criminals to national law.

Nonetheless, given that legal incentives for OAGs to comply with IHL in NIAC are already so tenuous, the intrusive transnational criminalization of terrorism further weakens them. This may not seem like much, but when the stakes are so high – more violence against civilians, against an already high background level – minimizing intrusion is worth it. This is true even of many “terrorist” groups, whether Al-Shabaab, Hamas, the Taliban, the Kurdistan Workers’ Party (Partîya Karkerên Kurdistanê, PKK) or the Liberation Tigers of Tamil Eelam (LTTE) (or even exterminatory groups such as the Khmer Rouge), since experience suggests that, at some point in a conflict, some group members may be willing to engage directly or through back-channels with external interlocutors and values,Footnote ⁵⁴ and group behaviour may eventually respond.

A second, related reason to be cautious about criminalizing OAG hostilities as terrorism relates to the relationship between sovereignty and IHL in NIAC. As mentioned, in NIAC the affected State has long enjoyed the sovereign right under national law to criminalize members of OAGs for offences against national security or other interests, whether labelled as terrorism or otherwise. However, the transnational criminalization of terrorism in conflict is distinguishable from prior practice. NIACs were traditionally civil wars fought by citizens in a State's own territory, not the more complex transnational NIACs of today. The right to criminalize conduct was thus closely linked to the State's sovereign territorial jurisdiction over its own territory and population. The exercise of extraterritorial criminal jurisdiction by one State over the conduct of OAGs in another State was a rarity, limited by the necessity of identifying an acceptable basis for extraterritorial prescriptive jurisdiction under international law. One such basis was universal jurisdiction over war crimes under IHL treaties and customary IHL. In the absence of a jurisdictional basis, States generally did not criminalize foreign civil wars, and they refused to cooperate with the territorial State in suppressing its domestic political opponents (by upholding the political offence exception to extradition for classic civil war “crimes” such as rebellion, revolution and sedition). Foreign civil wars will usually not affect a State's own security or involve its nationals as perpetrators or victims, so as to attract other jurisdictional grounds.

The expansive jurisdiction now asserted over terrorism offences has broken the historical nexus with a sovereign's presumptively territorial rights.Footnote ⁵⁵ It has also been accompanied by the depoliticization of terrorism offences in extradition, prompted by the later ICTCs and UN standard-setting since the late 1990s. Under the ICTCs, this is less problematic, because their carefully defined offences are limited in subject matter (they largely do not criminalize conduct not already prohibited by IHL, and do not criminalize civilian DPH or “material support” to terrorist groups), and because they are often subject to armed conflict exclusion clauses (discussed below). Treaty-making processes, open to all States, ensured that IHL was taken into account.

In contrast, more general terrorism offences under Resolution 1373 are not guided by any agreed international definition but are creatures of unilateral national implementation; they do not accommodate IHL through any exclusion formula at all; and they are imposed on all States by a fifteen-member-State Security Council (the Permanent Five of whom matter), without the opportunity for all States to participate or to ventilate their concerns about IHL. For these reasons, States should be very cautious before defining terrorism to encompass participation in hostilities in foreign NIACs. Even where a State's own forces are involved in the foreign conflict, that State is not the territorial sovereign with a general competence to prescribe the criminal law applicable there, and it does not enjoy any equivalent of the powers of an occupier in IAC, which would allow it to enact security offences in foreign territory.Footnote ⁵⁶ At most, it may potentially (and controversially) assert expansive security/protective jurisdiction.

It is one thing for a State to suppress non-State violence which challenges its own political authority in its own territory, but quite a different proposition for it to suppress – by choice, or even by obligation – political violence (not violating IHL) in another State's territory. The latter would interfere, on the side of the foreign government, in foreign domestic political struggles – this was historically avoided by applying the political offence exception in extradition law and treaties (itself now increasingly eliminated), and was even celebrated, as in the case of foreign volunteers in the Spanish Civil War. Foreign suppression of non-State violence abroad further undermines incentives for OAGs to comply with IHL, who are painted into a corner as “terrorists” everywhere. This does not, of course, detract from the right of States to criminalize “foreign recruitment” or enlistment offences – now recast as “foreign fighter” travel offences – in order to prevent their own nationals or residents from travelling to participate in conflict abroad.

A third broad reason to be circumspect about CTL is that it may impede other IHL-related interests during a conflict. In extreme cases, some States may deny that IHL applies at all to “terrorists”, whether because they do not wish to legitimize “terrorist” groups by admitting the existence of an armed conflict,Footnote ⁵⁷ or because they claim that IHL rules in conflicts they do recognize do not apply to individual “terrorists”, or apply in “overly permissive” ways.Footnote ⁵⁸ The legal and political polarization of relations with “terrorist” groups may also make such groups suspicious of engaging with humanitarian actors, particularly if the latter are seen as part of the international community's counterterrorism apparatus – this may be because of their perceived closeness to major counterterrorism powers (including through co-option in the service of militarized stabilization, or development-oriented civilian “hearts and minds” campaigns); because of their contractual or other legal requirements to report suspicious behaviour to governments; or because UN agencies are part of the “whole of UN” approach to counterterrorism under the UN Global Counter-Terrorism Coordination Compact of 2018 and its Coordinating Committee, and under the sweeping “Pillars” of the UN Global Counter-Terrorism Strategy of 2006.

A fourth broad reason for caution about overlaying CTL onto IHL relates to cessation of conflict. The “extreme vilification” of classifying OAGs as terrorists can seriously hinder the political willingness or legal ability of governments to enter into peace negotiations in order to end conflicts, as occurred with the FARC-EP in Colombia.Footnote ⁵⁹ These hurdles to “negotiating with terrorists” can add to the usual barriers encountered in armed conflicts. They can also affect the scope of negotiations and the nature of the post-conflict settlement or reconciliation,Footnote ⁶⁰ particularly regarding the treatment of “terrorist” fighters. IHL encourages States to confer the widest possible amnesty for (IHL-compliant) acts during conflict.Footnote ⁶¹ If an OAG has been labelled or its members criminalized as terrorist, it may complicate the willingness of governments to issue amnesties, as well as the acceptability of such amnesties to socially divided populations that have been hardened to fear “terrorists”.

Relatedly, CTL can complicate or frustrate the eligibility of persons for disarmament, demobilization and reintegration (DDR),Footnote ⁶² which may be necessary for a lasting peace. UN DDR standards emphasize that neither those suspected of terrorist acts nor individuals or groups listed by the Security Council can be eligible for DDR, as is the case for those suspected of international crimes.Footnote ⁶³ However, the standards operate by renvoi to the definition of terrorism not only in the ICTCs but also in Security Council resolutions, which do not define terrorism and allow States to decide the issue, including whether to criminalize mere membership in or support for an OAG, or participation in hostilities, even when not prohibited by IHL. Exclusion from DDR can thus be over-broad: terrorist offences in national law are not necessarily of equivalent gravity to international crimes warranting exclusion from DDR. The same is true of excluding anyone associated with a Security Council listed group, which in itself does not reveal anything about any harmful conduct of individuals. The UN standards note, however, that DDR knowledge may be relevant to implementing the “prosecution, rehabilitation and reintegration” measures which the Security Council has indicated should be used in relation to foreign terrorist fighters.Footnote ⁶⁴

Whether, and the extent to which, CTL adversely impacts on IHL in armed conflict depends on the definition and scope of particular CTL rules, including any exceptions for IHL. The next section reviews the pros and cons of various exceptions and considers which approaches are capable of optimally balancing CTL and IHL interests.

International counterterrorism conventions, 1963–2020

Of the nineteen ICTCs adopted since 1963, only one (on hostage-taking) prior to 1997 expressly addressed IHL, whereas since 1997 IHL has been addressed in all instruments: a limited exception in the Terrorist Financing Convention of 1999, and a common exclusion of armed forces in armed conflict in six other instruments (discussed below). The latter exclusion is also the basis of negotiations for the Draft UN Convention since 1999.

Most ICTCs only apply where an offence has a transnational element, thereby excluding purely domestic acts in a NIAC. However, the transnational element under most ICTCs includes situations where an offender is present in another State or, depending on the instrument, where victims or perpetrators are nationals of States other than the place of commission, a foreign aircraft or ship is affected, or another State is subject to compulsion. As such, conduct in an otherwise localized NIAC may still come within the ICTCs.

Silence on IHL

The earlier ICTCs do not address armed conflict but often have implications for IHL. Six ICTCs adopted between 1963 and 1988 addressing aviation and maritime safety do not apply to aircraft or ships used for military, customs or police services,Footnote ⁶⁵ military air bases,Footnote ⁶⁶ or (by implication) military maritime platforms.Footnote ⁶⁷ The Nuclear Material Convention of 1980 likewise applies only to peaceful uses of civilian material, thus excluding attacks on military nuclear material. The exceptions were not designed to accommodate IHL but reflect the civilian mandates of the fora within which they were negotiated (the International Civil Aviation Organization, International Maritime Organization, and International Atomic Energy Agency).Footnote ⁶⁸

The effect of the exceptions is that attacks on military aircraft, ships, airports, platforms or nuclear material during armed conflict are not covered by the ICTCs and are instead regulated by IHL. Such acts are excluded regardless of the status of the attacker (whether State forces or OAGs, or civilian DPH) and whatever the means or methods used (whether IHL-compliant or not). Conversely, attacks on civilian objects are co-regulated by the ICTCs and IHL (including any war crimes). Where attacks are unlawful under both regimes (as where a civilian aircraft is deliberately targeted), conflict of laws is negligible.

In contrast, there may be a prima facie conflict of obligations where an act is lawful under IHL but unlawful under an ICTC. For example, it could be lawful to target a civilian cargo vessel also carrying military munitions or personnel for a party to a conflict, whereas it is an ICTC offence to destroy a ship or damage it or its cargo if likely to endanger the ship's safe navigation. Similarly, it could be lawful under IHL to target military aircraft parked at a civilian airport where proportionate damage to a nearby civilian aircraft may be expected, whereas it is an ICTC offence to intentionally destroy a civilian aircraft or damage it and thereby render it incapable of flight.Footnote ⁶⁹ Collateral damage to the civilian aircraft is still “intentional” in that the military aircraft was attacked with knowledge or awareness that the civilian aircraft would be damaged and the attacker also meant to bring about that result.

The two regimes thus impose potentially incompatible obligations. One answer is to invoke one or the other regime as the “hard” lex specialis to trump the other. The difficulty is that “it is often hard to distinguish what is [relatively] ‘general’ and what is ‘particular’”:Footnote ⁷⁰ the particular IHL rules because they are adapted to armed conflict, or the aviation or maritime safety convention offences because they are tailored to protect civilian aircraft or ships?

A possible solution to this question is found in the ICTCs themselves. The aviation and maritime safety conventions, like many ICTCs, define conduct as offences where the conduct is not only “intentional” but also “unlawful”. During the drafting, “unlawful” was intended to refer to grounds under national law which could justify or excuse offences, such as in legitimate law enforcement operations or personal self-defence. There was little attention to whether international law, including IHL, could also be used as a standard; it certainly could be if incorporated into national law. It is arguable that the ICTCs should be harmoniously interpreted with IHL by applying the IHL rules to define whether an act is “unlawful” under the ICTC; if not, no CTL offence is committed. This approach applies the “soft” version of lex specialis, as in the Nuclear Weapons Advisory Opinion (where a flexible human rights standard – the meaning of an “arbitrary” deprivation of life – was interpreted in light of an IHL rule). Such an approach is also preferable because the drafters of the aviation and maritime safety conventions did not intend to displace IHL; they simply did not consider it (whereas later revisions of those instruments explicitly defer in part to IHL).

The Protected Persons Convention of 1973 does not address armed conflict and is the one ICTC which potentially raises a direct and irreconcilable conflict with IHL. It requires States to criminalize the murder, kidnapping, or “other attack” on the person or liberty of an internationally protected person (such as a diplomat), as well as any “violent attack” on their official premises, private accommodation or means of transport.Footnote ⁷¹ The Convention deliberately corresponds with the strict inviolability of diplomats and diplomatic premises under the Vienna Convention on Diplomatic Relations (VCDR) of 1961.Footnote ⁷²

In most situations, there will be no conflict under the Protected Persons Convention. In principle, diplomats are civilians, not combatants or fighters, and diplomatic premises and vehicles are civilian objects, and are all immune from attack under IHL. There are examples in practice where breaches of inviolability were also likely IHL violations.Footnote ⁷³ Problems arise, however, if a diplomat takes a direct part in hostilities; or an embassy becomes a military objective by hosting combatants or persons taking a direct part in hostilities; or an embassy suffers proportionate collateral damage from a strike on a nearby military objective. All such intentional attacks would be offences which States Parties must prosecute under the Convention, whereas IHL may permit targeting (and confer combatant immunity in IAC). Unlike the aviation and maritime conventions, the 1973 Convention does not refer to “unlawful” acts and thus provides no avenue to harmoniously apply IHL rules. In addition, the difficulty with taking a hard lex specialis approach is again deciding which regime is special: IHL, as adapted to armed conflict, or the 1973 Convention, because it is tailored to protect diplomats and embassies?

Under international law, the inviolability of diplomats and embassies is strict, admitting no exceptions even for serious violations of local law, abuses of diplomatic functionsFootnote ⁷⁴ (including espionage or political interference), or emergencies.Footnote ⁷⁵ The appropriate remedy within the purposefully self-contained regime of diplomatic relations law is a declaration of persona non-grata, expulsion of the mission, or suspension/termination of diplomatic relations in general.Footnote ⁷⁶ There is no clear authority that even personal or national self-defence would excuse a breach of inviolability. There is thus little room to accommodate IHL. IHL equally signals its own comprehensiveness. Even where IHL accords special protection to certain persons or objects (medical, humanitarian, cultural or religious; works containing dangerous forces; or objects indispensable to civilian survival), it never accords absolute immunity from attack or precludes proportionate casualties. There is thus no room in IHL for absolute diplomatic inviolability.

Thus far the sparse State practice has not provided an answer on resolving conflicts, although some practice suggests that inviolability prevails over IHL,Footnote ⁷⁷ consistent with its absolute character in other areas. Israel defended attacks on inviolable UN Relief and Works Agency premises in Gaza (for instance, in 2008–09 and 2014) on IHL grounds (either as military objectives used by Palestinian fighters, or as proportionate casualties of strikes on nearby military objectives). In response, UN Boards of Inquiry insisted on the inviolability of UN premises,Footnote ⁷⁸ which “could not be overridden by demands of military expediency”,Footnote ⁷⁹ while emphasizing that IHL co-applies to protect civilians inside UN premises.Footnote ⁸⁰ The Eritrea-Ethiopia Claims Commission likewise upheld the absolute inviolability of an embassy, even if it had been used to “criminally” stockpile weapons for the war effort;Footnote ⁸¹ while it did not specifically address IHL, its reference to “absolute” inviolability was emphatic, in a context where it was mandated to apply IHL in an IAC between two States and was thus aware of IHL's possible relevance. While the Convention on the Safety of United Nations and Associated Personnel of 1994 excludes certain UN “combatants” from its offences concerning attacks on UN personnel, this does not imply an IHL exception to inviolability since only very senior UN personnel (equivalent to diplomats or above), not UN peacekeepers, are entitled to inviolability in the first place.Footnote ⁸²

Whether such an approach is desirable, from a policy standpoint, is debateable. A strict approach minimizes the risks of States abusing IHL (or other legal) rights and thereby endangering not only the person or premises of diplomats or other protected persons but, through them, the all-important channels – especially in war – of inter-State diplomatic communication. On the other hand, it is precisely in conflict that States could be tempted to abuse inviolability in order to further their war aims (for instance, to relay military information or coordinate local subversives) – although an embassy in the adversary's territory makes an easy target for a military response, rendering such misuse both unwise and unlikely. The remedies of diplomatic relations law – persona non grata, expulsion of a mission, or suspension/termination of relations – may not be timely against threats which necessitate an immediate military response (although a law enforcement approach may often suffice). Clarity could be provided by an amendment to the Protected Persons Convention (whether prioritizing inviolability over IHL or vice versa), but this is unlikely precisely because the Convention is predicated on diplomatic relations law and seeking an amendment would reopen controversies over exceptions to inviolability in general.

The Draft UN Convention

Despite being agreed in the six ICTCs in 1997, 2005 and 2010, the exclusion clause has remained controversial during the negotiations for the Draft UN Convention since 1999. The Organisation of Islamic Cooperation (OIC) proposed excluding the activities of the “parties” – rather than “armed forces” – during armed conflict, “including in situations of foreign occupation”.Footnote ¹⁴⁶ This proposal is partly the result a technical difference over the proper terminology – “parties” aims to include OAGs, given the disagreement over the meaning of “armed forces” – but it also stems from a political disagreement about the desirable scope of the exception.

Both “armed forces” and “parties” are IHL terms of art. Only States are referred to as (high contracting) “parties” to IHL treaties,Footnote ¹⁴⁷ which not only regulate their “armed forces”Footnote ¹⁴⁸ but also impose obligations on the wider entity of the State (to legislate, disseminate, prosecute, cooperate and so forth). In NIAC, common Article 3 separately refers to “each Party to the conflict” in order to denote State and non-State parties; the latter are not also High Contracting Parties, however, since only States are parties to treaties.Footnote ¹⁴⁹ Common Article 3 then guarantees protections for, inter alia, “members of armed forces” no longer taking an active part in hostilities, necessarily meaning both State and non-State forces. To the extent that the OIC's reference to “parties” aims to counter those States which narrowly interpret “armed forces” as only State militaries,Footnote ¹⁵⁰ it is redundant on a proper interpretation of “armed forces” under common Article 3.

However, the OIC also intends the term “parties” to exclude actors other than members of OAGs. These could conceivably include disorganized armed groups,Footnote ¹⁵¹ sporadic civilian DPH (without performing a CCF and thereby being members of an OAG), or civilians supporting hostilities without taking a direct part therein. Self-determination movements and OAGs, for example, typically comprise not only armed wings but also wider (and often larger) political and social organizations, some of which may also engage in violence with a nexus to the conflict. In practical terms, reference to the “parties” is aimed at exempting entities such as the Palestine Liberation Organisation, Hamas, Islamic Jihad and Hezbollah.Footnote ¹⁵² The EU was concerned about the implications of excluding activities of the “parties” in Northern Ireland and Basque Spain,Footnote ¹⁵³ mirroring concerns that India had about Kashmir, although some of these concerns presuppose an expansive understanding of self-determination beyond colonial situations and to which AP I may not extend.

It is highly doubtful, however, that replacing “armed forces” with “parties” would make any difference (unless “armed forces” are limited to those of the State, as Jordan believedFootnote ¹⁵⁴). A non-State “party” to a NIAC is exclusively constituted by an OAG. There is no equivalent recognition under IHL of any other components of a non-State party, such as the political, civil or administrative arms of a wider anti-government movement. In contrast, as mentioned, “States Parties” mean not only their armed forces (including irregular forces) but also other State organs (such as police and intelligence agencies) and other persons or entities attributable to States under the law of State responsibility. The OIC proposal makes a distinction without a difference because a non-State “party” to a NIAC is the same entity as an OAG – that is, the non-State “armed forces”.

The more difficult question – pertinent also to the six prior ICTCs with the exclusion clause – is who or what comes within the scope of the non-State “party”/OAG/“armed forces”. There was little discussion of the precise scope of non-State “armed forces” during the drafting of the ICTCs, largely because the meaning of this term was left to IHL. Yet the concept defining who comprises such forces (OAGs), under IHL itself, is open to debate. On a narrow view, the category includes only members of the group performing a CCF. On a middle view, it includes any member of the group, whether performing a CCF, persons otherwise (sporadically) taking a direct part in hostilities, or persons taking an indirect part in hostilities via support for the group (such as “police” or intelligence elements which may facilitate military operations without taking a direct part in them). On the widest view, it includes all of the preceding actors as well as others associated with the group who neither take a direct part in hostilities nor otherwise support hostilities (without taking a direct part therein). These could include the purely civil or administrative components of an armed movement which controls territory and governs a population, such as birth registrars, bureaucrats, police or judges. A narrow focus on fighters evidently does not account for the complex totality of certain non-State movements.

The dominant (and correct) approach is that “in respect of armed groups with multiple wings and/or divisions, reference to the armed group is usually to the military wing of the armed group”Footnote ¹⁵⁵ (even if there may be humanitarian costs to this approachFootnote ¹⁵⁶). This means that any exclusion of the activities of non-State “armed forces”/“parties” would only exclude fighters (CCF) or, on a slightly wider approach, other members integrated into the OAG and supporting hostilities but without taking a direct part therein.

IHL already stipulates consequences for such conduct, including targeting and security detention, and does not preclude liability for national crimes. The exclusion debate is thus partly a political struggle over what should be labelled as terrorism or not, rather than an attempt to confer impunity on “terrorists”. However, to the extent that ICTC offences differ from IHL or international criminal law in establishing additional liabilities, conferring wider powers or requiring distinctive international cooperation, the disagreement is also a legal one.

Civilians sporadically taking a direct part in hostilities, or who otherwise support hostilities (without taking a direct part therein), are still covered by ICTC offences, even if they are associated with the wider civil or administrative structures of a non-State movement. Importantly, these could include civilian policing or intelligence elements which use violence with a nexus to the conflict, without being members of the OAG.

The OIC's further proposed exclusion of “foreign occupation” is legally redundant in that an occupation is, by definition, an IAC under Article 2 common to the four Geneva Conventions, regardless of whether there are also hostilities between State forces.Footnote ¹⁵⁷ The wording of the OIC's proposal (conflict “including” occupation) recognizes as much. OAGs involved in concurrent hostilities in occupied territory, and which do not “belong” to the occupied State, may separately be “armed forces” in a NIAC and also be excluded from the ICTCs. Since the OIC formulation is limited to “armed conflict, including … foreign occupation”, strictly speaking the provision does not appear to address a wider, non-IHL notion of “occupation”, for instance relating to non-self-governing territories or incomplete or contested decolonization.

Security Council obligations on States to criminalize terrorist acts

Beyond the ICTCs, Security Council Resolution 1373 requires all States to criminalize “terrorist acts” and various preparatory acts (including terrorist financing), while subsequent resolutions have required criminalization of other conduct relating to, for example, so-called “foreign terrorist fighters”.Footnote ¹⁵⁸ The Council has not, however, provided a common international definition of such acts, and nor has it unequivocally prescribed the relationship of offences to IHL (such as through exclusion clauses, as in the ICTCs). Although its non-binding 2004 “working definition” addresses IHL in limited ways (by renvoi to predicate ICTC offences, and applying only to acts against “civilians”, thus excluding acts against fighters),Footnote ¹⁵⁹ it has had little influence on State practice. The Council's CTL monitoring bodies (the Counter-Terrorism Committee and Counter-Terrorism Executive Directorate) have also not publicly disclosed any clear position.

The risk is that national implementation of the Security Council's CTL offences (as well as terrorist financing measures) may violate IHL (particularly by undue restriction, prohibition or criminalization of medical and humanitarian activities, including contact or dialogue with OAGs) or infringe on IHL policy values (by criminalizing direct participation in hostilities or membership of OAGs). While the Council has not expressly required States to criminalize such activities, the risk of States doing so is heightened by factors such asFootnote ¹⁶⁰ the Council's lack of definition of terrorist acts, the potentially wide ambit of offences such as “support” for terrorist acts, and direction from the Council to criminalize the financing of “terrorist” individuals or groups “for any purpose”Footnote ¹⁶¹ (not only for the commission of terrorism, as under the Terrorist Financing Convention), in conjunction with a vague definition of “funds” as “any assets” (tangible or intangible, moveable or non-moveable, and thus not limited to pecuniary funds).Footnote ¹⁶² A further risk lies in the requirement to criminalize the travel of “foreign fighters”, which, while limited to travel for the purpose of participating in terrorist acts (not merely to participate in hostilities), was nonetheless adopted in the context of armed conflictsFootnote ¹⁶³ in Syria and Iraq and in the absence of any limiting definition of terrorism.

Positively, the Security Council has gradually become more attuned to IHL. In Resolution 1373, the Council did not insist on State compliance with international law when implementing CTL obligations, other than in the context of refugees.Footnote ¹⁶⁴ However, since 2005 the Council has routinely reminded States of their duty to comply with all of their obligations under international law, specifically including (among others) IHL, when implementing CTL obligations.Footnote ¹⁶⁵ Admittedly, many references have been preambular, or in operative but non-binding paragraphs, or confined to measures in a particular resolution.Footnote ¹⁶⁶ Since 2019 one resolution has made IHL compliance binding (“decides”),Footnote ¹⁶⁷ following a trend pioneered in respect of human rights in 2017.Footnote ¹⁶⁸

These limitations should not, however, be understood as indicating that the Council's binding CTL measures may override IHL unless IHL consistency is expressly affirmed, whether in relation to the criminalization of terrorist acts or asset freezing under Resolution 1373 (where IHL is not mentioned). There is a presumption against normative conflict under international law, including in the context of the Security Council's power under Article 103 of the UN Charter to “override” inconsistent international agreementsFootnote ¹⁶⁹ (and there is doubt as to whether Article 103 can override custom at allFootnote ¹⁷⁰). In an analogous human rights context, in Al Jedda v. UK (2011), the European Court of Human Rights held that, in interpreting Security Council resolutions, there is “a presumption that the Security Council does not intend to impose any obligation on member States to breach fundamental principles of human rights”; the interpretation must be chosen “which is most in harmony with the requirements of the [other obligation] and which avoids any conflict of obligations”; and the Council must use “clear and explicit language” to override another obligation.Footnote ¹⁷¹ The same applies to IHL,Footnote ¹⁷² which also comes within the UN's purpose of respect for “human rights” (writ large) under Article 1(3) of the UN Charter.Footnote ¹⁷³

The Security Council has not indicated a clear intention to override IHL.Footnote ¹⁷⁴ To consider pertinent examples, when criminalizing “support” for or “financing” of terrorist acts under Resolution 1373, the Council did not specify that this must encompass medical or humanitarian personnel, or activities or assets protected by IHL (including medical care for injured “terrorists”) – just as the Council's authorization of security detention in Al-Jedda did not indicate that due process need not be observed. Indeed, the IHL implications of Resolution 1373 simply did not occur to the Council at the time. The Council has not criminalized contact, engagement, dialogue or association with terrorist groups for humanitarian, IHL, human rights or peace-making purposes. When later criminalizing financing “for any purpose”, the Security Council resolution expressly “decided” that IHL must be respected. Criminalization of foreign terrorist fighters focuses on their travel to participate in terrorist acts, but the Council did not criminalize mere participation in hostilities, let alone humanitarian or medical activities.

The listing of two persons and two entities by the Security Council under the Resolution 1267 regime seemingly (in part) for medical activitiesFootnote ¹⁷⁵ also does not indicate a clear intent to override IHLFootnote ¹⁷⁶ (in that context of terrorist financing sanctions). Those listings were based mainly on serious terrorist activity: for example, Redendo Cain Dellosa led the SuperFerry 14 attack by Abu Sayyaf in the Philippines which killed 100 people; Zafar Iqbal was a senior leader and co-founder of Lashkar-e-Tayyiba; and the Global Relief Foundation raised large sums for Al-Qaeda operations. No conclusions can be drawn from the reasons for listing as to whether the very briefly mentioned medical activities were, on the facts, of a kind even protected by IHL; and there is no evidence that the sanctions committee considered, and chose to override, IHL before mentioning those activities. Further, as discussed in the next section, the omission of an express medical or humanitarian relief exception to CTL measures also does not support an implication that the Council clearly intended to override IHL.

The better view is that States must implement CTL obligations in conformity with IHL, which the Security Council increasingly appears to recognize as the lex specialis – and not vice versa. Moreover, as the next section indicates, IHL itself accommodates many of the security-related concerns which CTL seeks to address, further reducing any potential for conflicts. It is, rather, the legislative choices made by States, often with purported reliance on Security Council resolutions, which collide with IHL, rather than the measures adopted by the Council itself.

Relationships between CTL and IHL in national practice

Given the decentralized nature of implementation of Security Council CTL obligations, which are both undefined and not subject to unambiguous IHL clauses, it is no surprise that national and regional practice is highly variable as regards the relationship between CTL and IHL.