The recent revelations of a UK drone strike in Syria targeting British individuals alleged to be linked to the Islamic State has generated much discussion, and the British government has presented the foundations of what it perceives as the legal basis for this strike under international law. The UK’s statements thus far provide the beginning of the answer as to the legal basis for resort to force on Syrian territory without its consent. It remains, however, to be seen whether the Government considers the UK to be in an armed conflict against the Islamic State, separate from the Iraq-Islamic State conflict, and will provide a law of armed conflict (LOAC) analysis as to why the individuals targeted did not have civilian protection. Alternatively, the government would need to demonstrate how such killings could be justified in light of the strict restrictions on use of force in the law enforcement framework. While the current UK approach has many echoes of past US positions, the US arguments tended to include statements to the effect that it was in armed conflict with al-Qaeda and therefore relying on the LOAC framework to justify targeting individuals (whether or not these statements were accurate was a subject of debate). This new case of the UK operation presents one of the first and clearest examples of a drone strike against individuals which may have occurred — seemingly by the state’s own account — outside of an existing armed conflict. Either that, or the UK may have just claimed to be in a new armed conflict against IS. One way or the other, this is a remarkable turn of events which may have significant legal repercussions.

Both the basis presented for the strike and much of the discussion surrounding it have been mired in confusion over a number of legal principles. The following is an attempt to untangle the legal threads and present the key issues as far as international law is concerned. The most crucial legal questions that must  be addressed deal with the legal basis for using force in Syrian territory without its consent (the jus ad bellum), and the legal basis for the act of killing individuals by direct recourse to lethal force.

Use of Force in Syria Without Consent

The first question goes to the heart of the UN Charter provisions on resort to force. Outside of UN Security Council authorization, the only other legitimate basis for resort to force in the territory of another state is self defense. The drone strike, as reported, embodies what may be the two most contentious issues in this area. First, is the question as to whether states can invoke self defense in response to armed attacks by a non-state actor, and on this basis use force against that armed group in the territory of another state, without the latter’s consent. While my view is that self defense does encompass action against armed groups abroad, I also recognize that this is an unsettled matter in the eyes of many states and commentators, and if accepted it must be interpreted narrowly.

The second matter is the unfinished debate over the use of anticipatory self defense — whether a state can engage in self defense force in advance of an armed attack or whether it can only do so after an attack has begun. The arguments over this have been around ever since self defense by states was first presented as a legal right and there continue to be strong arguments by both sides. Support for anticipatory self defense is generally thought to exist only in relation to the need to prevent an imminent attack. The meaning of “imminence” has been stretched and pulled in all directions, especially in relation to countering transnational terrorism and weapons of mass destruction. If imminence is to be accepted as the standard for anticipatory self defense it must be understood as limited to situations of an impending attack over which there is a reasonable level of certainty that it will occur in the foreseeable future, and it must be a specific and identifiable attack, rather than a vague threat of unknown form. This question will remain nearly impossible to address publicly until more is known about the planned attacks that the British government claims those killed in the strike played a role in.

Use of Lethal Force Against Individuals

The above rules can provide the answer in relation to the resort to force on Syrian territory without its consent. They are designed to govern questions of force and protection of sovereignty in the relations between states. In other words, they tell us when a state is allowed to resort to force on the territory of another state. But, they tell us nothing about how the force can be used. For example, the resort to force by a state against another state might be legal, but the way it uses force might still include commission of war crimes. To analyze the question of the actual force against individuals and in particular the direct recourse to lethal force, there are two potential legal frameworks: the law of armed conflict (also referred to as international humanitarian law), and the law enforcement framework as found in international human rights law.

Under LOAC, certain individuals may be targeted by direct recourse to lethal force on account of either their status or their function and specific activities. There has been much debate over the interpretation of the rules governing loss of civilian protection and lethal force in armed conflict, and whether geographical location affects an individual’s status. It is however relatively clear that in certain circumstances, LOAC will allow for direct lethal force against individuals if specific criteria are fulfilled.

Nonetheless — and this relates to a crucial and unusual facet of the UK operation — for LOAC to apply, the operation must be occurring as part of an armed conflict. Outside of an armed conflict, LOAC simply does not apply. Interestingly, the Prime Minister has the following to say: “I want to be clear that this strike was not part of coalition military action against ISIL in Syria – it was a targeted strike to deal with a clear, credible and specific terrorist threats to our country at home.” While the reason for this declaration was likely due to domestic concerns and previous parliamentary debates in relation to the UK’s involvement in this conflict, this means that either the UK believes it is currently in the midst of a separate armed conflict against the Islamic State, or that this drone strike was taken outside of an armed conflict. If it is the former, it is hard to see how — once we set aside the Iraq-Islamic State conflict — the violence between the Islamic State and the UK would pass the intensity threshold to be considered a separate armed conflict.

Although the Prime Minister referred in his words to military rules of engagement and the operation was conducted by the military, if the strike was not taken within a specific armed conflict then the recourse to direct lethal force against individuals cannot rest upon the rules of LOAC. These rules would simply be inapplicable outside of armed conflict. The only other legal framework that provides guidance on the circumstances in which a state might use lethal force against individuals is found in law enforcement and international human rights law. This legal framework does not rule out lethal force. It does however set a much higher bar, in which force cannot be the first option and lethal force is an act of last resort, to be taken only in exceptional circumstances (for example, if an armed robber is holed up in a bank executing hostages and the only way to stop this is for a police sniper to take a head shot). The comments by UK Defence Secretary Michael Fallon appeared to say that the legal framework under which the individuals were killed is similar to the one used by police in law enforcement. Indeed, in this video he compared this operation to the same “basis on which armed police can use force on our streets to prevent the potential loss of life.” The necessity and proportionality aspects of the case will require very close scrutiny, and here too the notion of imminence and the concern that it does not get distorted is a key factor (see Principle 9 of Use of Force and Firearms by Law Enforcement Officials).

If it is indeed the law enforcement framework that was relied upon, this has interesting implications for the debates over extraterritorial applicability of international human rights law. Many states have argued that international human rights obligations should not extend to forcible operations outside of the state’s own territory. When these operations occur in the context of an armed conflict, this approach gets conflated with the endless debates over the interplay between human rights and LOAC. They are separate issues, and even after accepting extraterritorial applicability of human rights law, there remains a need to work out the precise nature in which the two frameworks apply concurrently and how they might influence the interpretation of each other.

However, if a drone strike takes place outside of an armed conflict, then there is no interplay since LOAC doesn’t apply — a state cannot rely on the inapplicable LOAC to justify the taking of life. Such a situation presents a perfect example of why international human rights law does not stop at state borders, and certainly in relation to the deliberate taking of life, it may in some circumstances be the only applicable framework for determining legality. It cannot be the case that outside of armed conflict states are free to kill individuals extraterritorially with no governing rules. This is not to say that human rights law would automatically prohibit the taking of life (even through drone strikes), but it does present a high threshold that could only be crossed in the most exceptional of circumstances. If this strike is not going to be an isolated incident, one would hope that the UK government lawyers have started preparing their human rights based response, as the litigation is undoubtedly on the way.

Editors’ Note: An earlier version of this post mistakenly quoted David Cameron as saying the strike in question was not part of coalition military action against the “Islamic State in Support of Iraq”  The post has been updated to correctly read “against ISIL in Syria.” Just Security regrets the error.