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On Preventive Killing

Published on September 17, 2015        Author: 

If we wait for threats to fully materialize, we will have waited too long. We must take the battle to the enemy, disrupt his plans and confront the worst threats before they emerge. In the world we have entered, the only path to safety is the path to action. And this nation will act.

George W. Bush, 17 September 2002.

It seems to me that there are two different ways of understanding the targeted killing of UK citizens Reyaad Khan and Ruhul Amin by a Royal Airforce-piloted drone on 21 August 2015, in Raqqa, Syria. (Khan was the target of the strike, and Amin was also killed by it. Both Khan and Amin are described as “ISIL fighters.”)

The first poses some difficult constitutional and public law questions for the UK government, but does not require any kind of radical re-interpretation of international law governing the use of force.

The second way of understanding the strike amounts to a sea change in the UK’s legal position, and indeed aligns it with several US legal positions in the “war on terror” which, hitherto, no European state has formally embraced.

Prime Minister David Cameron’s statement is ambiguous about the exact legal basis of the strike. However, in contrast to the seemingly deliberate admixture of jus ad bellum and jus in bello rationales offered by leading Obama administration officials (Koh 2010 ASIL Speech; Holder 2012 Northwestern University speech), Cameron clearly uses the language of Article 51 of the UN Charter. He refers to the UK’s “inherent right to self-defence” and “clear evidence” that these two individuals were “planning and directing armed attacks against the UK … [which were] part of a series of actual and foiled attempts to attack the UK and our allies.” Finally, Cameron contends that the strike was authorized because “there was no alternative.”

Let me first turn to a way of understanding this strike which does not raise exceptionally controversial legal issues (although nothing seems very settled these days!). As Dapo points out in his post of 11 September, from an international law standpoint, the UK is already in a non-international armed conflict with ISIL, as part of a collective self-defence action on behalf of the Government of Iraq. To the extent that this conflict spills over into Syrian territory and Syria has effectively lost all control over some parts of its territory governed by ISIL (and Raqqa would meet that test), it seems to me that one does not need any additional ad bellum justification, specific to the UK, to attack ISIL fighters in their Syrian stronghold.

On the collective self-defence theory, what matters is not whether these individuals pose a specific threat to the UK, but simply whether ISIL members directly participating in hostilities can be directly targeted on Syrian territory, because Syria is unable to prevent ISIL from launching armed attacks on Iraq from its territory. (While the “unable or unwilling” test remains very controversial, few states appear to have contested the specific extension of strikes against ISIL in Syria (and indeed, Syria has not protested vigorously either)). On this argument, the two UK citizens killed exercised a continuous combat function rendering them targetable in the on-going armed conflict between the coalition of states assisting Iraq and ISIL, which has been extended to Syrian territory on the grounds that Syria cannot any longer control that territory and prevent ISIL attacks. The point is that the UK does not have to bear that particular argumentative burden alone. In its letter to the Security Council explaining its use of force, the UK in fact relies on both the claim of individual self-defence and the claim of collective self-defence on behalf of Iraq.

Cameron’s language concerning the UK’s inherent right to self-defence, and the necessity and proportionality of this specific strike, could perhaps be best understood as intended to overcome the serious UK domestic constitutional law problem that the Parliament voted to authorize UK participation in strikes against ISIS only in Iraq, and not in Syria. During the debate on that vote, on 26 September 2014, the Prime Minister sought to reserve to the government a discretion to strike within Syrian national territory “if there were a critical British national interest at stake or there were a need to act to prevent a humanitarian catastrophe”. In those circumstances, “you could act immediately and explain to the House of Commons afterwards. I am being very frank about this because I do not want to mislead anybody.” (Hansard, 26 September 2014, column 1265). Thus, Cameron’s elaboration now of a self-defence argument seems tailored to satisfying the House of Commons and the British public that he was acting properly within the discretion reserved to the executive to act in response to an urgent threat emanating from Syrian territory, even if this action exceeded the authorization granted by the Parliament in its vote of 26 September.

Whatever his political calculations, the legal argument implied by Cameron’s justification for the targeted killing of a UK citizen and the ancillary killing of another, takes us down a much more controversial route: it aligns the legal position of the UK closely with a subset of legal arguments made by the Obama administration (continuing in important respects a posture adopted by the George W. Bush administration). Let us parse a little further the wording of Cameron’s statement:

Both Junaid Hussein [killed in a US airstrike on 24 August] and Reyaad Khan were British nationals based in Syria who were involved in actively recruiting ISIL sympathizers and seeking to orchestrate specific and barbaric attacks against the West, including directing a number of planned terrorist attacks right here in Britain, such as plots to attack high profile public commemorations, including those taking place this summer.


There was clear evidence of the individuals in question planning and directing armed attacks against the UK. These were part of a series of actual and foiled attempts to attack the UK and our allies.

Mr. Speaker, our intelligence agencies identified the direct threat to the UK from this individual. They informed me and other senior ministers of this threat … [W]e agreed that should the right opportunity arise, then the military should take action.

This statement seems crucially ambiguous on whether the individual was targeted because he was currently directing an armed attack in the process of being executed, or whether, because he had consistently planned (foiled) attacks in the past (“including those taking place this summer”), he constituted by his profile and record of activity an on-going threat to the UK. Similarly ambiguous is whether what was “disrupted” by the strike was another developing attack, or more simply, the individual’s life and thus any future opportunity to plan an attack. Finally, as seemingly implied by the phrase “should the right opportunity arise,” it appears that the RAF were pursuing the target for some time before finding the right window to strike. It is also reported that other UK citizens have been placed on a “kill list,” including Mohammed Emzawi, the alleged “Jihadi John” responsible for decapitating ISIL hostages in several Islamic State propaganda videos.

It does not require an intellectual historian to trace the lineages of this legal rationale. It bears a close resemblance to the arguments advanced by former Foreign Office Legal Advisor Sir Daniel Bethlehem in his 2012 note in the American Journal of International Law. Bethlehem himself maintained that his Note was an attempt to synthesize and clearly formulate principles which were to be derived from counter-terrorist practice of governments, ‘largely away from the public gaze.’ It is not clear which and how many governments are engaged in practices conforming to such principles, and in his Note Bethlehem draws on public statements only from the US and the UK. But the lineaments of Cameron’s rationale would appear to conform to some of Bethlehem’s formulations, and also certain key arguments made by the Obama administration in its justification for the targeted killing of US citizen Anwar al-Awlaki (the so-called Department of Justice White Paper)

The first concerns the extended concept of “armed attack,” to include a series of planned terrorist attacks, imminent or actual, which cumulatively are deemed to amount to an armed attack (imminent or actual) giving rise to a right to armed action in self-defense against those “actively planning, threatening, or perpetrating armed attacks” (AJIL Note, 775). Bethlehem points out that some support has gathered for the so-called pin-prick theory of armed attack, in the context of state’s cross-border use of force against non-state armed groups (referring in particular to Christian Tams’ important EJIL article from 2009).

As Wilmhurst and Wood (AJIL 107:393-4) observed in response to Bethlehem’s note, the pin-prick theory remains controversial. But the framing of a series of planned terrorist attacks – far removed in this case from any territorially proximate armed conflict with a non-state armed group on the borders of the state claiming self-defence – is an extended version even of the pin-prick theory and goes beyond the concrete type of situation in respect of which it was invoked. As is well-known, the pin-prick theory had its origins in attempts by the US, Israel, Portugal and South Africa to justify what might otherwise have been a disproportionate use of force against national liberation movements or armed guerilla fighters operating across an adjoining international border (the US invoked this argument in respect of its claim to be engaged in collective self-defence on behalf of South Vietnam). To divorce the pin-prick theory from any dimension of territorial proximity and delimitation, seems to me to radicalize it in a way that dissolves any distinction between a domestic criminal act of terrorism (such the July 7, 2005 bombings in London or the 11 March, 2004 bombings in London) and a contribution to a casus belli under the jus ad bellum. Distinguishing between these two categories would become, then, a question of closely held intelligence about actual, planned, or perhaps even inchoately hoped-for attacks, making a state’s claims difficult if not impossible to objectively evaluate and verify.

The second debt to the Bethlehem principles (Principle 8) and the DOJ White Paper evident in the Prime Minister’s statement is an extended concept of imminence. The necessity of striking Khan is explained as the “only feasible means of effectively disrupting the attacks planned and directed by this individual.” Self-evidently, killing Khan was not the only way of disrupting his planned attacks because British security services are also stated to have foiled more than one attack on the UK or its allies. So the concept of imminence here is not in the sense of “interception” of an unfolding plot. Rather, the Prime Minister’s language intimates that killing Khan was necessary because it was the only way to stop him trying again. As such, evaluating the “imminence” of the threat posed by Khan would appear to be in the nature of a probabilistic risk assessment of his (high) propensity to plan and direct another terrorist attack in the UK; by virtue of his pattern of activity, his very continued life constituted an imminent risk. Also included in this extended concept of imminence is whether other opportunities to kill the target will present themselves, should he not be targeted now. The language of the DOJ White Paper is perhaps more explicit about this than the Bethlehem principles, but in my view they boil down to the same position:

First, the condition that an operational leader present an “imminent” threat of violent attack against the United States does not require the United States to have clear evidence that a specific attack on U.S. persons and interests will take place in the immediate future … Consequently, with respect to Al-Qa’ida leaders who are continually planning attacks , the United States is likely to have only a limited window of opportunity within which to defend Americans in a manner that has both a high likelihood of success and sufficiently reduces the probabilities of civilian casualties … Furthermore a “terrorist war” does not consist of a massive attack across an international border, nor does it consist of one isolated incident … It is a drawn out, patient, sporadic pattern of attacks. It is very difficult to know when and where the next incident will occur.

… By its nature, therefore, the threat posed by Al-Qa’ida and its associated forces demands a broader concept of imminence in judging when a person continually planning terror attacks presents an imminent threat, making the use of force appropriate. In this context, imminence must incorporate considerations of the relevant window of opportunity, the possibility of reducing collateral damage to civilians, and the likelihood of heading off future disastrous attacks…

… A high-level [US] official could conclude that an individual poses an “imminent threat” of violent attack against the United States where he is an operational leader of Al-Qa’ida or an associated force and is personally and continually involved in planning terrorist attacks against the United States … and there is no evidence suggesting that he has renounced or abandoned such activities …

Several aspects of this concept of imminence are noteworthy. First, the concept of imminent threat – terminology drawn from the debate over the legality of anticipatory self-defence within the UN Charter framework – is here radically subjectivized (that is, made the quality or characteristic of an individual subject). It becomes a question, as noted above and evident in the language of Cameron’s statement, about whether this person’s continued existence amounts to an on-going threat, even if we cannot identify a plan to attack at this moment; past conduct and continued intention are decisive. Second, the logic of the targeting rationale is not “interceptive” (to use Dinstein’s terminology, Yoram Dinstein, War, Aggression and Self-Defence, 4th edition, Cambridge, 2005, p.191) or even “anticipatory” in the sense of the various archetypal scenarios against we are accustomed to measure the meaning of this term (see, for example, the cases discussed by Gray in her cautious treatment: Christine Gray, International Law and the Use of Force, 3rd edition, Oxford, 160-64). Rather, the logic is preventive.

It is often noted that anticipatory self-defence vis-a-vis state actors remains controversial and uncertain. But it seems to me that preventive killing of the kind claimed to be legally justified by Cameron, is not a version of anticipatory self-defence; rather it amounts to a new kind of claimed exception to the Article 2(4) prohibition on the use of force, an exception predicated on a legal argument in which the lines between crime and casus belli, terrorism and armed attack, criminal and enemy, state war and non-state war, are deliberately blurred – with the result that the conceptual distinctions that have hitherto formed a fragile scaffolding by which we have differentiated between defensive force, and something else, are hollowed out and transformed to licence a kind of conflict that (on both sides) destroys these distinctions.

Preventive killing is, self-evidently, a kind of manhunting. It rests not only on an asymmetry of means and methods of warfare, but also on a thick juridical asymmetry: one side, the state claiming self-defence, has complete legal and political personality, protected by international law as a bearer of jus ad bellum rights and duties. On the other side, the targeted person is at once criminal and military threat; they may have a legal equality vis-a-vis other persons as a bearer of human rights, but these are highly attenuated by their purported subsumption under the jus ad bellum as an “imminent threat”. To the extent that one’s pattern of conduct and continued presumed intention to plan terrorist attacks render one’s life by its nature an imminent threat, one’s right to life is highly conditional.

This juridical asymmetry has consequences for what we understand to be the purpose of the strict limits placed on the use of force by the Charter framework. The framework protects states’ right to defend themselves, but balances this with the aim of restraining as much as possible uses of force which could escalate into larger conflicts. As such, the Charter framework presumes and indeed requires that temporary defensive uses of force between states can be quickly subjected to peaceful forms of dispute resolution, where the underlying clash of interests leading to the outbreak of conflict can be mediated or even adjudicated. All of this presupposes the legal symmetry of states, and that each state’s interests have in principle the possibility of being recognized and negotiated, as means of containing the use of force. It is in light of this logic that we might understand the strict conceptualizations of armed attack and imminent threat that have governed the orthodox understanding of self-defence: states are not considered to have implacable and inevitable enmity towards each other (even if they are perpetual competitors or ideological enemies), but rather capable of changing their positions, even at the 11th hour, in light of the changing constellation of forces being brought to bear upon them that may affect their understanding of their interests and how best to achieve them.

Preventive killing is not assimilable to this logic. The targeted individual is not expected to change their views or their perception of their interest; at best, they may remove themselves from ongoing participation in the armed activities of the terrorist group, out of fear. But even this seems unlikely and indeed unexpected by those charged with evaluating the individual’s status as a target. There is no dispute with this individual to be resolved as a way of short-circuiting the use of force; there is only a threat to be disrupted, and a constant vigilance concerning the emergence of new such threats must be maintained.

With at least 500 British citizens estimated to be fighting with ISIL since 2014, the number of individuals that could in principle be targetable on this basis is not negligible, entailing a more or less perpetual posture of readiness for preventive killing. Other states with significant numbers of citizens who have joined ISIL over the last 12 months, such as France, have also indicated that they are preparing strikes to address threats to France.

Apart from Syria, other ungoverned territories may be included among those states in which there are no feasible options for arrest or detention – Libya, Mali and Somalia are easily susceptible to such categorization. With no risk of inter-state retaliation from such weak states, and the real prospect that killing militants said to threaten national security may be politically popular at home (given also that no military personnel are put at direct risk in such operations), the temptations of preventive killing as a policy option are numerous. But we ought to be under no illusion that – practised like this, and justified in these terms – it represents anything but significant alteration to how we have hitherto understood the law governing the use of force.

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3 Responses

  1. Jack McDonald


    Great article! If possible, could you clarify who or what the plural pronoun “we” refers to in the latter half of the piece? (“This juridical asymmetry has consequences for what we understand to be the purpose of the strict limits placed on the use of force by the Charter framework.”, “…it represents anything but significant alteration to how we have hitherto understood the law governing the use of force.”)

    The reason I ask is that I think if this refers to legal opinion beyond states, then I’d agree, but if it refers to the legal opinion of states, then I think the situation might be more nebulous. In the latter case, I think elements of legal asymmetry/manhunting* might, to certain states, simply be the logical application of existing principles to the threat posed by individuals that are now in a position to pose a threat from afar due to changing technology. The question then turns to how states understand their obligations and therefore what the AG’s advice was (which, in my opinion, should have been published).

    Secondly, I’m not sure that we can infer that he was not currently involved in a plot from Cameron’s speech (much in the same way that I’m unaware of any publicly available evidence that he was currently involved in a plot). From Cameron’s language, this could justify an attack on an individual that had planned an attack that was being prepared by others, but that required the original planner to coordinate. One theoretical example would be a single person (“A”) coordinating 5 individuals to commit attacks at the same time when the 5 others are unaware of the identity or plans of each other while they prepare individual attacks. In this case, A would remain an integral component of the operation, even though the planning and commission of attacks would be down to the 5 others. The ability of A to coordinate attacks in this fashion would perhaps allow 5 individuals to cause far more damage in a coordinated fashion than individual attacks alone. Whether or not that would be reason to kill A is, well, another discussion. I think, though, that on a conceptual level it is quite possible for individuals far away to be integral to operations/attacks in the UK.

    *In case you haven’t encountered it, you might want to check out Gregoire Chamayou’s stuff on manhunts/drones. I think his legal interpretations are terrible, but it’s an interesting perspective nonetheless.

  2. Jordan

    The quote from GW Bush reflects an outrageous, widely denounced, and unacceptable claim to use preemptive self-defense (e.g., re: an “emerging” threat that is not even a threat, much less threat of imminent armed attack), as opposed to a minority claim to engage in anticipatory self-defense when an armed attack is imminent — both contrary to the text of Article 51 (which recognizes the inherent right of self-defense “if an armed attack occurs” cf. the French version). What Cameron stated regarding directing armed attacks and other forms of direct participation fits neatly within the text of Article 51 (“if an armed attack occurs”, especially if one uses a movie camera to identify ongoing direct participation in armed attacks over time, as opposed to use of a snap shot at merely one point of relevant time (a significant error or some textwriters). See, e.g., (Operationalizing Use of Drones Against Non-State Terrorists Under the International Law of Self-Defense), an article that also debunks the so-called “unwilling or unable” limitation of the inherent right of self-defense against non-state actor armed attacks emanating from another state. See also and .
    A NIAC? hardly. It is an armed conflict of an international character in several respects. See, e.g., ibid. Otherwise, UK combatants would not have combatant immunity for lawful acts of war and would be subject to prosecution for murder, manslaughter, etc. under relevant domestic laws.
    Concerning direct participants in armed attacks (those who under the self-defense paradigm are DPAA) and who have a continuous armed attack function (those who under the self-defense paradigm have a continuous armed attack function), see ibid., esp. Operationalizing Use of Drones….

  3. Jordan

    p.s. Jack’s hypo is a good example of DPAA. Person A is coordinating armed attacks by others, which is direct participation in the armed attacks. Further, have the armed attacks begun? Is the “preparation” such that the armed attacks are actually underway? Further, are they part of a process or “series” of armed attacks over time (using a movie camera instead of a snapshot). Cameron’s phrase “part of a series of actual and failed attempts to attack” can relate to a series of actual attacks that nevertheless failed to result in their contemplated outcomes (the attacks had actually begun but were “foiled”).