U.S. Airstrikes in Syria and Iraq: Legal Authorities and Presidential War Powers

Late on Sunday, June 27, the Biden administration authorized U.S. airstrikes against facilities used by Iran-backed militias along the Iraq-Syria border. This was the Biden administration’s second airstrike along the Iraq-Syria border, and the strike comes as Congress is debating changes to existing Authorizations for the Use of Military Force (AUMF). This article unpacks known details of the strike, some of the legal issues involving the claimed authorities under international and domestic law, and how these justifications relate to ongoing debates on AUMF reform and presidential war powers. While the Biden administration refrained from using either the 2001 or 2002 AUMFs in its recent airstrikes, its exclusive reliance on executive power places stress on Article II constitutional authorities and underscores the need for an updated AUMF. The reliance on Article II authorities becomes particularly concerning if the United States continues airstrikes as part of an escalating tit-for-tat response to attacks on U.S. troops and facilities in the region, attacks that have only continued in the past week.

Q1: What were the airstrikes, and why were they conducted?

A1: The airstrikes targeted “operational and weapons storage facilities” at three locations, two in Syria and one in Iraq, near the towns of Al Bukamal and Al-Qa’im along the shared border between the two states. F-15E and F-16 aircraft carried out the strikes that reportedly killed four Iraqi fighters with the Iranian-aligned proxy Hashd Al-Shaabi. This strike closely follows the form of the Biden administration’s first authorized use of force on February 25, which was conducted by F-15E aircraft targeting nine facilities used by Iranian-backed militia groups located in Abu-Kamal, Syria, on the Iraqi border.

The Biden administration stated that the facilities targeted on June 27 had been used by Iranian-backed militia groups, including Kata’ib Hezbollah and Kata’ib Sayyid al-Shuhada, to conduct a series of unmanned aerial vehicle (UAV) and rocket attacks against U.S. facilities and personnel stationed in Iraq. The specific attacks were detailed in the White House’s subsequent letter to Congress, issued as consistent with the War Powers Resolution.

Several of the militia UAV attacks have been previously reported on and fit within the broader pattern of Iranian-backed militias using rocket attacks and drones to target U.S. personnel and facilities in Iraq. The White House’s recent letter stated that the attacks have injured and threatened U.S. and coalition personnel, although no deaths were mentioned.

Q2: On what legal authorities were the strikes conducted?

A2: The primary legal justifications are laid out in a Department of Defense (DOD) statement from June 27, the president’s letter to Congress on June 29, and a June 29 letter to the UN Security Council from the U.S. ambassador to the United Nations. 

The statements claimed the strikes exercised the United States’ inherent right of self-defense under international law, as laid out in Article 51 of the UN Charter. Under domestic law, the DOD statement argued that the airstrikes were conducted pursuant to the president’s Article II constitutional authority to protect U.S. military personnel. The president’s letter also refers to this authority, claiming that the strikes were conducted “pursuant to my constitutional authority to conduct United States foreign relations and as Commander in Chief and Chief Executive.” Both the domestic and international legal justifications are consistent with the Biden administration’s legal justifications used for its February 25 strike against Iranian-backed militias operating in eastern Syria.

Q3: Can these airstrikes be considered self-defense under international law?

A3: The claim that the airstrikes were exercising the inherent right of self-defense raises several legal questions regarding what qualifies as self-defense under international law, and there is an ongoing debate among legal scholars on whether the previous strikes in February qualified as self-defense. While some argue that the airstrikes in response to attacks by Iranian-backed militias fall within defensible interpretations of the inherent right of self-defense, others hold that they are unlawful because the strikes come after the attacks, being effectively an armed reprisal if there is not a threat of imminent or ongoing attack. Skepticism about claims of self-defense is warranted, especially as this justification has become increasingly common since the establishment of the UN Charter.   

In its public statements, the Biden administration took pains to address these concerns by emphasizing that the June 27 strikes were not in response to an isolated attack but rather in response to an “ongoing series of attacks” that have “escalated in recent months” and military action was taken to “disrupt and deter such attacks.” In making this argument, the president’s letter details the recent pattern of escalating attacks:

Rocket attacks:

  • Balad Air Base on April 4, April 18, and May 3, 2021
  • Baghdad Diplomatic Support Center on May 2, 2021
  • Al‑Asad Air Base on May 4 and May 24, 2021

UAV attacks:

  • U.S. facilities in Erbil on April 14, 2021
  • Al-Asad Air Base on May 8, 2021
  • Bashur Air Base on May 10, 2021
  • U.S. facilities near Baghdad International Airport on June 9, 2021

Highlighting this pattern of repeated attacks helps establish their ongoing nature and strengthens the justification that the airstrikes were made in self-defense.

The statements further stress the significance of sending an unambiguous signal to deter future attacks. The White House letter was explicit that the strikes were to “deter the Islamic Republic of Iran and Iran-backed militia groups from conducting or supporting further attacks on United States personnel and facilities” and was “directed at facilities used by groups involved in these ongoing attacks for weapons storage, command, logistics, and UAV operations.” These statements make it clear that the strikes were aimed to deter and dissuade future attacks, while also targeting the militia’s facilities in an effort to disrupt and degrade their ability to continue launching UAVs and rockets. By characterizing the strikes as being in part a deterrent against future attacks, the Biden administration does wade into thornier issues of anticipatory self-defense and whether any future attacks qualify as an imminent threat. However, taken in combination with the effort to demonstrate the ongoing nature of the attacks, the Biden administration strengthened its case that the airstrikes strikes were defensive in nature. 

Q4: Did the targeted states provide consent for the United States to strike targets within their borders?

A4: Neither Iraq nor Syria have said they consented to the airstrikes taking place on their territory. While the White House does not claim that the airstrikes were conducted at the invitation of Iraq, the DOD statement did note that the United States was “in Iraq at the invitation of the Government of Iraq for the sole purpose of assisting the Iraqi Security Forces in their efforts to defeat ISIS.” Iraq has since condemned the strike in harsh terms as a violation of international law. This lack of consent was previously raised by some scholars as an issue with the Biden administration’s first strike on February 25, which took place in Syria without its consent.

Absent the target states’ consent, the unwilling or unable test is often used, which holds that states are allowed to use force against threatening non-state groups in sovereign states either unwilling or unable to suppress them. This principle has experienced growing support internationally, and the United States has explicitly supported it in the past. The Biden administration mentioned the test in its previous letter to Congress for the February 25 airstrikes, and while it may apply this time, the test is notably absent from the most recent letter to Congress for the June 27 airstrikes.

Q5: How do the recent airstrikes relate to current debates on AUMF reform?

A5: Neither the Biden administration’s June or February strikes invoked the 2002 nor 2001 AUMFs, which are currently being debated by Congress. The White House has since doubled down on its domestic Article II authority for conducting the airstrikes, while simultaneously affirming its desire to work with Congress on AUMF reform to “update authorization parameters and legislation.”

Because one of the targeted facilities was in Iraq, the absence of any reference to the 2002 AUMF authority is particularly notable. The 2002 AUMF, passed by Congress before the 2003 invasion of Saddam Hussein’s Iraq, authorizes the use of force against the “continuing threat posed by Iraq.” This was subsequently used by the Obama administration as part of the legal basis for its campaign against ISIL and by the Trump administration for its strike against Qassem Soleimani on January 3, 2020. The absence of any reference to this authority is consistent with Biden’s commitment to updating AUMF authorities and support of legislation recently passed by the House to repeal the 2002 AUMF. The Biden administration’s Statement of Administrative Policy (SAP) further made it clear that there are no ongoing military operations that use the 2002 AUMF. The 2002 AUMF thus remains the low-hanging fruit in the attempt to reform AUMF authorities. That is not to say that efforts at repeal are insignificant. The successful repeal of the 2002 AUMF would be the first repeal of wartime authorities in 50 years.

The 2001 AUMF, which authorized the use of force against the terrorist groups behind the 9/11 attacks, was also not cited in either the February 25 or June 27 strikes. The 2001 AUMF undergirds much of U.S. counterterrorism operations but is outdated and has been subject to expansive interpretations over the past 20 years to include a number of groups with little or no ties to those behind the 9/11 attacks. This makes the 2001 AUMF the most important authority to update and reform, which the president has agreed to in principle.

Q6: Are Article II constitutional authorities adequate for these airstrikes? 

A6: By not citing the 2002 or 2001 AUMF authorities, the president is relying exclusively on his own Article II executive authority for these airstrikes against Iranian-backed proxies.

While it is admirable that the president is not continuing to stretch congressional authorizations enacted nearly 20 years ago against different actors, the exclusive reliance on Article II puts more pressure on executive authority. Article II authority has generally been interpreted by presidential administrations to allow short, limited uses of force, but the reliance on executive authority without congressional authorization invites pushback from Congress, especially as U.S. involvement becomes more substantial and drawn out. The recent airstrikes do fall short of other more prominent examples of force authorized under Article II authority that include, as John Bellinger noted in recent testimony before Congress, using force in Somalia in 1992, Haiti in 1994, Bosnia in 1995, and Libya in 2011. While the February and June airstrikes may still fall within Article II authority, this position may become unsustainable if the strikes escalate into a more substantial and prolonged conflict.

This is a real risk if the airstrikes continue and evolve into an ongoing campaign against Iranian proxies in Iraq and Syria. While the DOD statement explicitly states that the strikes were a “deliberate action designed to limit the risk of escalation,” UAV and rocket attacks by Iranian-backed militia are likely to continue. U.S. troops located in northeast Syria came under rocket fire the day after the airstrikes, and U.S. troops and facilities in Iraq and Syria have since come under continued and escalating rocket and UAV attacks this past week. By engaging in a tit-for-tat response, the United States may become involved in a pattern of limited uses of force that stretches Article II authorities and effectively constitutes a campaign of military action without authorization from Congress.

Senator Chris Murphy (D-CT) expressed this concern, stating that while the Biden administration may have the authority to defend U.S. forces, “repeated retaliatory strikes against Iranian proxy forces are starting to look like what would qualify as a pattern of hostilities under the War Powers Act. Both the Constitution and the War Powers Act require the president to come to Congress for a war declaration under these circumstances.”

Congress should continue to follow these airstrikes closely for potential escalation. As congressional leaders consider AUMF reform, they should also ask for the Biden administration’s view on where the threshold is for when a number of airstrikes reach a level that requires congressional authorization for the use of force.

Overall, the recent strikes by the Biden administration do not have the same escalatory significance as last year’s strike on Soleimani or involve the same legal stretch as invoking the 2002 AUMF. However, they do underscore the need for updated AUMF authorities to reflect current threats, contemporary actors, and present geopolitical realities.

Adam Saxton is a research associate with the International Security Program at the Center for Strategic and International Studies in Washington, D.C.

Critical Questions is produced by the Center for Strategic and International Studies (CSIS), a private, tax-exempt institution focusing on international public policy issues. Its research is nonpartisan and nonproprietary. CSIS does not take specific policy positions. Accordingly, all views, positions, and conclusions expressed in this publication should be understood to be solely those of the author(s).

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Adam Saxton