Armed Conflict Foreign Relations & International Law

The ETF and the Legality of U.S. Intervention in Syria under International Law

Douglas Cantwell
Monday, March 28, 2016, 9:28 AM

On Friday, the Pentagon announced that U.S. forces had killed senior ISIS commander Abd al-Rahman Mustafa al-Qaduli, known as “Haji Imam.” According to reports, U.S.

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On Friday, the Pentagon announced that U.S. forces had killed senior ISIS commander Abd al-Rahman Mustafa al-Qaduli, known as “Haji Imam.” According to reports, U.S. Special Forces were attempting to capture Haji Imam in eastern Syria when they fired on his vehicle, killing him and three others. The raid is another reminder that a small number of U.S. ground troops are on the front lines of the fight against ISIS. As acknowledged publicly late last year by Secretary Carter, the “Expeditionary Targeting Force” (ETF) was created to “accelerate” the fight against ISIS, in cooperation with Iraqi government and Kurdish forces. ETF operations across the Iraq-Syria border should reignite questions about the legality of U.S. intervention in Syria under international law, an issue largely overlooked since airstrikes began there in 2014. Failure to offer a more detailed international law argument is a missed opportunity for the U.S. to shape emerging norms on the use of force against non-state actors.

It has been clear since its formation that the ETF would undertake operations inside Syria. Secretary Carter stated:

These special operators will over time be able to conduct raids, free hostages, gather intelligence, and capture ISIL leaders. This force will also be in a position to conduct unilateral operations into Syria. (Emphasis added)

The ETF was established following a successful raid into Syria in May 2015, where U.S. Special Forces killed ISIS commander Abu Sayyaf and captured his wife, transporting her to Iraq for interrogation and detention.

The full extent of U.S. ground operations in Syria is unclear. In addition to an unsuccessful hostage rescue attempt and the raids on Haji Imam and Abu Sayyaf, there have been allegations of temporary control of an airfield (see Jonathan Horowitz’s legal analysis) and indications of operators joining allied forces in direct combat. More notable is a mission the ETF may be asked to conduct in the future. In his Atlantic article on the “Obama Doctrine,” Jeffrey Goldberg notes: “killing the so-called caliph of the Islamic State, Abu Bakr al-Baghdadi, is one of the top goals of the American national-security apparatus in Obama’s last year.” Like Haji Imam, Al-Baghdadi may be in Syria.

Since launching airstrikes in September 2014, the Obama administration has been mostly mum on its legal justification for operations inside Syria. While the U.S. and coalition partners may rely on consent of the Iraqi government for operations in Iraq, operations in Syria—whether airstrikes or special operations raids—potentially violate Article 2(4) of the UN Charter, prohibiting “the threat or use of force against the territorial integrity or political independence of any state….” Notwithstanding the debate over the legality of humanitarian intervention, traditionally, uses of force are legal only when the host government consents in advance, when the Security Council authorizes force under Chapter VII, or within the narrow confines of Article 51 self-defense.

Deadlock in the Security Council has left three potential justifications for operations in Syria: 1) consent of the Assad regime; 2) collective defense; and/or 3) self-defense against an imminent threat. The latter two require that the Syrian government be ‘unwilling or unable’ to address the threat posed by ISIS (a standard that U.S. allies have questioned, despite a history of state practice). ETF operations in Syria raise issues about the viability of each argument. The ETF also presents another potential argument for intervention: unit self-defense.


The Assad regime has not openly and expressly consented to U.S. operations in Syria and the Obama administration has emphasized that it did not “ask permission" before launching airstrikes. Ryan Goodman pointed out that the Assad regime may have impliedly consented. However, most of the statements cited in support refer explicitly to air operations, not ground troops, and were later repudiated. ETF operations most certainly don’t fall within implied consent based on recent statements. On February 6th, the Syrian Foreign Minister said that any ground intervention in Syria would be considered an act of aggression and that foreign troops would “return home in wooden coffins.” It will be worth noting what, if anything, the Assad regime says about the Haji Imam raid in the coming days.

It is possible the Assad regime privately consented to both U.S. airstrikes and special operations but, for diplomatic and political reasons, neither side has made this public (as was the case with the U.S. drone program in Pakistan). However, it seems unlikely that the U.S. would seek advance consent for cross-border ETF operations. As with the decision not to inform Pakistan prior to the bin Laden raid, informing the Assad regime of an impending mission might unnecessarily endanger U.S. personnel or forfeit the element of surprise, if word of the operation leaked.

Collective Self-Defense

The main theory the U.S. has relied upon for operations in Syria is collective defense of Iraq. Iraq explicitly requested assistance, following the formalities of declaring an armed attack on its territory and invoking Article 51 of the UN Charter.

Where the collective self-defense claim becomes controversial is in its application against ISIS. States routinely act in self-defense against non-state actors, but must show that the state in which the non-state actor is based is ‘unwilling or unable’ to address the threat. This was the argument put forward by Ambassador Power after airstrikes began in her Article 51 letter to the UN, which highlighted the threat ISIS’s safe havens in Syria posed to Iraq.

Accepting the legality of the unwilling or unable standard, the U.S. has a strong argument that the Assad regime has not effectively addressed the threat posed by ISIS, as others have discussed at length. The unable or unwilling standard requires: i) force used be necessary to protect against the threat; and ii) the amount and nature of force be proportionate to its suppression. The ETF may in fact strengthen the U.S. basis for intervention in Syria on the proportionality prong. Special operations raids are, in theory, more targeted than airstrikes. The ETF offers the ability to at least attempt a capture before resorting to strikes, as appears to have been the case in the Haji Imam strike.

For collective defense, the U.S. must show that ETF operations are necessary to protect against the threat to Iraq. This was a compelling argument when airstrikes in Syria began, with Iraq rapidly losing territory and ISIS advancing on Baghdad. However, as Ryan Goodman, Ashley Deeks, and Jennifer Daskal noted:

If the goal shifts from defending against, repelling, or containing ISIL to destroying ISIL … this legal ground becomes shakier. The United States (and Iraq) will need to establish that the destruction of the group is necessary and proportionate to the threat – something it very well may do, but which will likely raise questions about proportionality.

Iraq still faces a serious threat to its sovereignty; actions inside Syria remain necessary to its defense. The strategic aim of ETF operations – degrading ISIS’s ability to hold territory – is no less necessary to Iraq’s defense than airstrikes. But the Obama administration, if relying primarily on collective defense, may soon need to justify why it is necessary to the defense of Iraq to continue the campaign against ISIS in Syria.

National Self-defense

The U.S. has emphasized national self-defense to justify strikes in Syria as well as in Libya. While the requirements of the unable or unwilling standard must still be met, national self-defense requires the threat of an imminent attack on the United States or American personnel. When airstrikes in Syria began, self-defense was asserted for strikes against the now infrequently mentioned Khorasan Group. Close U.S. allies initially balked at participating in strikes in Syria, fearing there was an insufficient legal basis.

Self-defense has subsequently been invoked more frequently. As Bobby Chesney covered, the UK claimed self-defense to justify its airstrike targeting a British citizen, Reyaad Khan, in Syria in September 2015. The U.S. claimed self-defense for the November 2015 strike that killed Abu Nabil in Libya. France asserted self-defense following the Paris attacks. In light of the San Bernardino attack and threats of future attacks, the U.S. has re-emphasized self-defense. In April of 2015, then-General Counsel to the Department of Defense Stephen Preston stated:

In Syria, the United States is using force against ISIL in the collective self-defense of Iraq and U.S. national self-defense…Under international law, states may defend themselves, in accordance with the inherent right of individual and collective self-defense, when they face armed attacks or the imminent threat of armed attacks.... ISIL is a threat not only to Iraq and our partners in the region, but also to the United States. (Emphasis added)

Last month’s strike on an ISIS training camp in Libya was justified as necessary to prevent the spread of ISIS in Libya, which was “potentially planning external attacks on U.S. interests in the region.” The attacks on Brussels will no doubt provide additional impetus for states to invoke self-defense.

The ETF raises issues for U.S. self-defense claims. As Jonathan Horowitz noted, the definition of “imminent” used for strikes against ISIS looks less like that traditionally accepted under the Caroline standard and more like Bush-era pre-emptive self-defense. This interpretation was embraced by the Obama administration in the strike against Anwar al-Awlaki.

The ETF was touted as the cornerstone of efforts to “accelerate” the campaign to degrade and destroy ISIS, a goal grounded more in the law of collective defense of Iraq and the policy of preventive self-defense, not the imminence-based law of pre-emptive self-defense. This doesn’t mean that future ETF operations could not be justified under pre-emptive self-defense, based on an imminent threat. However, the ETF’s purpose to degrade ISIS through capture and kill missions will surely be invoked as evidence that the U.S. has continued to embrace a legal definition of imminence that encompasses preventive defense.

Unit Self-Defense?

Following the death of Staff Sergeant Louis Cardin, the Defense Department acknowledged that a “couple of hundred” Marines have deployed to northern Iraq. Attacks on the Marines at “Firebase Bell” raise the possibility that ETF operations in Syria could be justified under “unit self-defense.” Marines stationed at the U.S. outpost in northern Iraq are, along with the ETF, supporting local forces preparing to re-take Mosul. Unit self-defense, included in the standing U.S. rules of engagement, allows troops to defend themselves against imminent threats. As Erica Gaston explained, the U.S. interprets this right as derivative of the sovereign right of national self-defense.

Unit self-defense was invoked following the recent airstrike on al-Shabaab in Somalia, where militants were preparing to attack U.S. and AMISOM troops. Any claim that the threat of further attacks against the ETF and associated U.S. forces— or allied Iraqi and Kurdish forces—triggers the right to engage in unit self-defense in Syria would be controversial. However, a unit self-defense argument would eliminate the need to show an imminent threat to U.S. personnel elsewhere or to the U.S. homeland, requiring only evidence of an attack on troops in northern Iraq.


The Haji Imam raid and the likelihood of future cross-border ETF operations should lead to a better articulation of the U.S. argument for intervening in Syria under international law. While there was a flurry of critical analysis when airstrikes began in 2014, little has been said since the U.S. established a ground presence in northern Iraq and announced its intention to launch operations in Syria. International law arguments by the Obama administration have been few and far between. Secretary Carter’s comments following last week’s raid fail to even acknowledge that there may be different legal standards worth articulating, instead saying only that “[t]he removal of this ISIL leader will hamper the organization's ability for them to conduct operations both inside and outside of Iraq and Syria.”

The U.S. is not necessarily violating international law in Syria. There are colorable arguments that both airstrikes and special operations are necessary and proportionate in the collective defense of Iraq or in self-defense, based on Syria’s inability or unwillingness to stem the threat posed by ISIS. However, besides the Power letter and the Preston speech, the Obama administration has left observers scratching their heads. Failure to specify in detail the legal theories relied upon is a mistake for an administration that has touted its commitment to bring U.S. actions back in conformity with international law. This failure unnecessarily leaves the U.S. open to criticism that it is violating international law and is a missed opportunity to influence emerging rules for intervention, particularly in regard to the “unwilling or unable” standard. ETF operations should lead to a more detailed articulation of the legality of U.S. intervention in Syria.

Doug Cantwell is an International Law Fellow at the American Society of International Law (ASIL). He is currently on reserve status as an Ensign in the U.S. Navy Judge Advocate General's Corps. He received his J.D. from Columbia Law School, M.A. from the Graduate Institute of International and Development Studies, and B.A. from Stanford University. The views expressed here are his personal views and do not reflect those of the Department of Defense, the United States Navy, or any other department or agency of the United States Government. The analysis presented here stems from his academic research of publicly available sources, not from protected operational information. Any views expressed are those of the author and not those of the American Society of International Law.

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