The Killing of Soleimani, the Use of Force against Iraq and Overlooked Ius Ad Bellum Questions

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As most people know by now, the US killed Qassem Soleimani, head of the Iranian Quds force, in a drone strike on 3 January. Most commentators seem to agree that Soleimani’s killing was unlawful, but one issue has received less attention: the legality of using force against Iraq. The strike occurred in Baghdad, killing not only Suleimani but also five Iraqi nationals, including the leader and members of Kata’ib Hezbollah. This post examines the legality of the use of force against Iraq from a ius ad bellum perspective, arguing that a putative US claim to self-defense against Iraq stretches the doctrine of ‘unable or unwilling’ to breaking point.

The Legal Debate

The legality of the US drone strike has generated much debate. The US now argues that the strike is one among other actions taken ‘in the exercise of its inherent right of self defense… in response to an escalating series of armed attacks… by the Islamic Republic of Iran and Iran-supported militias’ (Article 51 letter to the UN Security Council). A major point of contention is the disputed claim that Iran (and Soleimani specifically) was planning imminent attacks against the US as well as the Trump administration’s evolving and contradictory understanding of ‘imminence’ for the purpose of self-defense against Iran.

It is not entirely surprising that there is a split in the legal commentariat. While some US-based lawyers (a minority even in the US, however) argue that the strike was lawful, I am not aware of any non-US lawyer who endorses the US administration’s evolving self-defense (or other) rationales (for more on the US’ latest legal arguments, see Adil Ahmad Haque). The legality of the strike under US law is less contested, but of course the strike remains illegal if it violated international law. Interestingly, states have been far more reluctant to question the legality of Soleimani’s killing.

One question that has received less attention in the blogosphere is the legality of using force against Iraq. By killing Soleimani, the US used force not just against Iran, but also against Iraq. Yet the Trump administration has not articulated any legal rationale for using force in Iraqi territory and against the five Iraqis, which raises additional questions about the strike’s legality under the ius ad bellum (this post does not address whether the killing of the Iraqis was lawful under IHL and human rights law, though that too deserves more scrutiny).

Using force against Iraq

The US has two ways to justify the use of force against Iraq: consent and self-defense (there is no Security Council authorization). Consent could, in theory, be relevant. US forces are currently stationed in Iraq, as part of the anti-ISIS coalition acting in the collective self-defense of Iraq, on the basis of Iraq’s consent. However, judging by its reaction to the strike, it is unlikely Iraq provided consent to this specific operation. In fact, the Iraq government appears to be so upset by the strike that it may have already withdrawn consent for the US’ presence in Iraq. On 5 January, Iraqi lawmakers voted to expel US forces, although uncertainty remains as to the legal validity of this vote (some suggest the vote is non-binding and must be implemented by the executive, others argue that the transitional administration does not have the authority to make such determinations). On 10 January, the Iraqi prime minister formally requested the US to prepare plans for the withdrawal of US troops, something I will return to later.

Can the strike be justified as an instance of lawful self-defense against Iraq? The answer to this question depends on the facts and specifically whether the five Iraqi nationals were also targeted in the drone strike. The Iraqi nationals killed in the strike were the leader and members of Kata’ib Hezbollah, an Iran-backed group which has attacked US bases in Iraq in recent months (triggering US counterstrikes against the group’s bases on 29 December, see Scott Anderson). One possibility is that on January 3, the US intended to target not only Soleimani but also the five Iraqi members of Kata’ib Hezbollah. This is legally relevant because, as explained by Crispin Smith, Kata’ib Hezbollah was recently integrated into the Hashd al-Sha’abi (Popular Mobilization Forces), making it an official organ of the Iraqi military.

This means that if the drone strike targeted the five members of Kata’ib Hezbollah, the US targeted not only an Iranian state representative but also members of the Iraqi armed forces. In this case, one potential legal justification would be to expand the US self-professed (self-defense) rationale against Iran and argue that self-defense also extended to the five Iraqis killed in the drone strike. As with the killing of Soleimani, the US would need to show that Iraq – specifically Kata’ib Hezbollah – was planning imminent attacks against the US.

However, the US government has not made this claim. As far as we know, the drone strike targeted only Soleimani and the US shifting and contradictory self-defense claim extends only to Iran. So the question remains: what is the US ius ad bellum justification for targeting Soleimani in Iraqi territory (and killing five Iraqi state agents to boot)? In his post, Marko Milanovic suggests that using force against Iraq can potentially be rationalized under ‘expansionist theories’ of self-defense:

…this situation would be analogous to self-defence against non-state actors – using force on the territory of the state in which the attacker is located would need to be justified by the necessity of stopping the attack, e.g. pursuant to an unwilling or unable theory. In other words, the US would need to demonstrate that it had to strike at Soleimani when and where it did, that it could not ask the Iraqi government for permission (e.g. on the basis of its collusion with Iran) and that it could not wait to strike at Soleimani elsewhere. 

I now examine the feasibility of justifying the US use of force against Iraq on the basis of ‘expansionist’ self-defense arguments grounded in ‘unable of unwilling’, while drawing attention to the legally problematic results this doctrine engenders.

Can the US invoke ‘unable or unwilling’ to justify using force in Iraq?

Answering this question takes for granted the expansionist ius ad bellum doctrine known as ‘unable or unwilling’ (U/U). The better view is that this controversial doctrine is rejected by most states. However, since the US is one of its proponents, I examine the doctrine’s potential applicability in this post. Though it dates back to the 1970s, U/U has re-emerged in the last twenty years as a means of invoking self-defense against non-state actors operating in the territory of non-consenting states who refuse (unwilling) or do not have the military/law enforcement capabilities (unable) to eliminate a threat originating in their territory.

Applying this doctrine to the US drone strike would look like this: despite the lack of Iraqi consent for this strike, the US exercised its right of self-defense against Iraq because using force in Iraqi territory was necessary – Iraq was ‘unable or unwilling’ – to prevent the threat from Soleimani. It is worth acknowledging that there are real questions as to Iraq’s ability and/or willingness to prevent Iran from launching an imminent attack (assuming one was being launched) from Iraqi territory. In particular, it is debatable to what extent the Iraqi government and its leaders can actually take decisions free from Iranian influence. Iran’s control of Iraqi proxy groups, including Kata’ib Hezbollah, seems beyond dispute. Were the US to articulate a self-defense claim based on U/U against Iraq, these factual questions would need to be carefully considered.

From a legal perspective, how is invoking U/U against Iraq to justify the Soleimani strike different from traditional U/U scenarios? For those who accept the doctrine’s validity, there are at least three nuances in this case: 1) Soleimani was a state actor (Iran) rather than a non-state actor; 2) the US is already operating in Iraq with Iraqi consent and 3) the attack also killed Iraqis and the victims were arguably state agents, rather than non-state actors. While none of these nuances makes a putative US self-defense claim based on U/U legally untenable, the implications of applying U/U to the Soleimani killing are troubling.

The first nuance poses no immediate problem, even though U/U is usually invoked against states harboring non-state actors in their territory. Harboring foreign state agents raises the political stakes, but I am not convinced it changes the U/U legal framework.

The same cannot be said about the second and third nuances.

The second nuance goes to the relationship between consent and self-defense as justifications for the use of force generally, and the scope of Iraqi consent vis-à-vis the US specifically. May the US use Iraqi consent for anti-ISIS operations in Iraq and, simultaneously, invoke self-defense against Iraq? Another way to think about it is: can Iraq both provide consent to US uses of force in Iraq and, at the same time, be deemed ‘unable or unwilling’ for the purpose of justifying other US uses of force in and against Iraq?

Crucially, a state consenting to the presence of foreign troops on its territory determines the scope of its consent to the use of force. According to the UN General Assembly, aggression is defined as (art. 3 e); see also ARSIWA, art. 20):

‘[t]he use of armed forces of one State which are within the territory of another State with the agreement of the receiving State, in contravention of the conditions provided for in the agreement or any extension of their presence in such territory beyond the termination of the agreement’

Even if Iraq had expressly declined consent for a use of force against Soleimani in its territory, it seems clear that the U/U would allow the US to circumvent this restriction. Under a U/U theory of self defense, the US can indeed argue that Iraq was ‘unable or unwilling’ to suppress the threat from Soleimani in Iraqi territory. It could even argue that refusing to grant the US permission to target Soleimani in Baghdad is evidence of Iraq’s unwillingness to address the threat. This type of argument leads to a troubling result: a consenting state no longer decides how far its consent to the use of force extends and what the invited state may lawfully do in its territory. Instead, the invited state, still nominally acting ‘at the invitation’ of the consenting state, decides for itself and effectively ignores the parameters of said consent by invoking the necessity of self-defense coupled with U/U.

The result is that U/U, applied in a context where the territorial State has already provided consent to the presence of the intervening State, effectively hollows out the ius ad bellum notion of consent. A deeply contested doctrine, such as U/U, makes consent, a universally recognized exception to the Charter’s prohibition of use of force, irrelevant.

Turning to the third nuance, it is worth reiterating that Kata’ib Hezbollah is an official Iraqi state organ. The US strike targeted an Iranian state representative but it also killed 5 members of the Iraqi armed forces (on the assumption, pending more information, that KH members were not targeted). It is surprising that this fact alone has not triggered more debate about the legality of the US strike. I suspect that is because commentators speculate Kata’ib Hezbollah is not really integrated into the Iraqi army (some may even speculate that Iraq did, in fact, provide tacit consent to the targeting of Kata’ib Hezbollah).

But let’s assume, for the sake of argument, that Soleimani had been met at the airport not by Abu Mahdi al-Muhandis and his Kata’ib Hezbollah colleagues but the Iraqi prime minister. The Iraqi prime minister has suggested that Soleimani’s trip to Iraq was to meet with him for the purpose of peace talks (disputed by US officials). Reports even suggest that there was a possibility Soleimani would be met by Iraqi government officials ‘allied with Americans’ (see Smith for more on this) at the airport. The same reports suggest that the US would have called off the strike had Iraqi officials such as the prime minister welcomed Soleimani, but the point is that these two situations – killing Kata’ib Hezbollah members and the Iraqi prime minister – are legally the same.

Taking the US self-defense coupled with U/U argument against Iraq to its logical conclusion means that the US could argue that it was necessary to target Soleimani (use force in self-defense against Iran) in Iraqi territory (use force against Iraq) because Iraq was ‘unable or unwilling’ to suppress the threat from Soleimani or consent to the use of force in its territory. Incredibly enough, if the Iraqi prime minister had incidentally been killed in the strike targeting Soleimani, the use of force against Iraq would still remain defensible on the basis of U/U, allowing the US to argue that there was no ius ad bellum violation vis-à-vis Iraq.

To be clear, I am not suggesting for a second that the US would have actually launched the strike against Soleimani if the Iraqi prime minister had welcomed him at the airport. The point is merely that under U/U doctrines of self-defense, such a strike would, potentially, not be a ius ad bellum violation vis-à-vis Iraq. This seems like an odd outcome, to put it mildly, and yet the US has not offered a legal rationale for why targeting Soleimani in Baghdad – alongside Iraqi state agents – was actually necessary.


While the Soleimani killing involves an unusual set of facts, occurring in a peculiar context of pre-existing consent, this case illustrates as well as any the troubling implications of U/U and should probably galvanize opponents of this doctrine. In the end, what is most remarkable about the Soleimani strike is the fact that the Trump administration has not even bothered to justify its use of force against Iraq. We do not know if the US actually thinks killing Soleimani in Iraq was justified on the basis of Iraq’s ‘unwillingness or inability’, but the still evolving legal rationales for targeting Soleimani raise serious questions about what role, if any, international law played in President Trump’s decision.

Trump’s disdain for international norms may eventually come back to haunt him. It is hard to see how the announcement that the US will not withdraw its troops from Iraq – despite Iraq’s revocation of consent – is anything but a textbook case of aggression, which further reinforces the perception that the Trump administration just didn’t think through the legal implications of its use of force. Then again, the reality is that we may simply be witnessing the next chapter in how far core international legal norms can be stretched in the Trump era.

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Nicolas Boeglin says

January 13, 2020

Dear Professor Labuda

Many thanks for this extremely useful analysis.

After the assassination of Qassem Soleimani, we all heard about official strong condemnations coming from Iraq, Iran, Syria, China, Russia, Turkey, Cuba an Venezuela.

The only State that officially congratulated US for this drone operation has been Israel.

However, considering EU members States and EU as itself, its seems that something does not allow them to condemn the target killing with an official drone of a top official from a State.

If I´m not wrong, it is the very first time that an official drone strike targeted a top official of a State: drone operations have usually targeted members of non state entities suspected of terrorism.

Do you have any idea in order to understand why in EU there is such a reluctance to condemn officially a clear violation of UN Charter in an official statement?

Yours sincerely

Nicolas Boeglin

John says

January 13, 2020

Nicolas Boeglin

EU reluctance is not new, have been there since Nato bombed Yugoslavia in breach with international law. EU - like the US - do not care about international law. They care about backing the US no matter what.
Besides Trump had terror-listed Soleimani/IRGC some months ago. A behavior which in turn have no basis in international law especially since Trump have produced zero evidence to begin to put Soleimani/IRGC on such a list.


January 14, 2020

Thanks for all of your comments.
According to the practice of the US, we need not be concern about ISIS or other terrorist groups. The US as a state commits terrorist acts. We as lawyers and law-researchers need to strengthen and reinforce the rule of international law serving humanity. The law on the use of force by States is clear: States shall refrain to use force and threat to it (the principle). The resort to use of armed force is allowed: by the authorization of the UN SC (Article 42) and in the case of self-defense (Article 51). Any other use of force is in serious violation of the UN Charter. Any practice against the principle and not justified under the two exceptions is violation of international law. It does not matter wich State and for what motive does it.
Another practice that weakens the rule of international law is the priority of US Constitution order over UN Charter order. The US decides who is a terrorist. So State X may decide that the US president or Secretary of State is a terrorist. This is the Jungle rule, it is not the rule of international law. So maybe it is the time to leave ISIS but be careful about the US,!!

Nicolas Boeglin says

January 15, 2020

Dear John

Many thanks for your very kind answer. Effectively we still are waiting for Soleimani´s "inminent" plans threatening US interests.

However, in 1999 NATO´s bombing of Serbia, some EU members where part of this joint military operation, but in the case of the assassination of Soleimani in Irak, its seems to me that only US took part to this killing, at least officially speaking (Israeli recent press note indicated that US intelligence services where helped: see it at

Sincerely yours

Nicolas Boeglin

Dr M Gandhi says

January 16, 2020

In the earlier analysis nothing is said about whether high ranking state official is protected in International Law or not and attacking him tantamount to attacking the sovereignty of State.
An analysis from this angle would reveal very clearly that the drone attack was violative of international law.

Javed Jiskani Baloch says

January 29, 2020

Apt debate but very narrow perspective legality of US action and very Broad view of Article 51... Those who say that killing of Soleimani by US Drone was a measure in self-defence must re-read the article again and they will find that this article invokes only when "an armed attack occurs". Even if an armed attack occurs, the injured state waits until the security council does something in collective self-defence. According to UNSCR 3314 (1974) "armed attack" is defined as "aggression", invasion, occupation, the annexation of territory, attack on armed personnel. ICJ in Nicaragua described self-defence as "an exception" (Paras 193-210) and in Oil Platform as "a qualification" (Para 43) Can anyone clarify whether Iran Invaded USA? or if did, why not to apply "effective control test" as established by Nicaragua case (1986).
Secondly, UNC article 2 (4) clearly mentions that the use of force which is against territorial integrity and sovereignty of the state and which is inconsistent with the purposes of UNO-peace, security, friendly relations, cooperation, and harmony among nations- as outlined in article 1 of UN Charter. I am afraid non of these defences fits well with what the US has done in Baghdad on 3rd January 2020-a very bad start of the year for the sake of winning some votes perhaps as many critics maintain because Abubakar al Baghdadi's recipe failed to create more curiosity at home so something unusual was required to solidify election campaign at home.

To me, it is a very bad precedent because what can we expect from underdeveloped and developing countries who we always try to convince for being good international citizens and abide by rules if so-called civilized and the powerful developed nations keeping making a mockery of the International law that already is under serious ethical and normative dilemma of millennial nature to sustain.