The Biden administration has recently engaged in a tit-for-tat fight with Iranian-supported Shia militias in Iraq and Syria. In the process, the administration is raising questions about whether it is following international and domestic law governing the use of lethal force.


On February 25, 2021, President Joe Biden ordered a strike on facilities in Syria operated by Iran-backed Shia militias. This was the first known new use of military force by his administration. (There were apparently two planned strikes, but one was halted at the last minute because a woman and children were seen at the location.) Within 48 hours, he sent a War Powers report to Congress in which he reported the attack and explained that the targeted groups “were involved in recent attacks against United States and Coalition personnel in Iraq, including the February 15, 2021, attack in Erbil, Iraq, which wounded one United States service member, wounded four United States contractors, including one critically, and killed one Filipino contractor.” The report asserted that “these groups are also engaged in ongoing planning for future such attacks.” The United States also submitted an Article 51 letter to the UN stating that the attacks were taken in self-defense.

It appears the groups may have now responded in turn with their own attack (in response to our attack in response to their attacks). On March 3, 2021, Al Asad air base in Iraq, where American and U.S.-led coalition forces are based, sustained rocket attacks. Iraq’s military, which runs the base, said the rockets caused no significant losses, but the Pentagon acknowledged that a U.S. civilian contractor died from a heart attack while sheltering. Pentagon Press Secretary John F. Kirby stated, “We cannot attribute responsibility at this time.”

To thicken the plot, the base that was the subject of the March 3 attack is the same base attacked by Iranian-backed militia after the Trump administration killed General Qasem Soleimani in Iraq in January 2020. That retaliatory strike did not lead to any deaths, but it did cause significant causalities: in particular, 50 American service members suffered brain injuries. Though there were fears at the time that the exchange could lead to all-out war between the two countries, the Trump Administration did not openly respond and the open exchange of fire came to a halt. Until now.

Just Security has already posted two strong pieces assessing the initial Biden administration strike. I will not repeat all the matters they cover, but I want to focus in on a few key issues.

Was the Biden Administration attack in Syria necessary?

Under international law, an act of self-defense must be proportional to the armed attack—meaning that there must be a congruency between the self-defense action and threat to be abated. An armed response must also be necessary to preventing future attacks.

Legal analysts often discuss whether an attack was “imminent.” Here, at least, the question of imminence is really, or rather, a question of necessity—is an attack so imminent that there is no reasonable alternative to the use of force. As Craig Martin has pointed out, there is a “difference between the truly necessary use of force to prevent and impede the continuing attack, and mere deterrence of a non-imminent future continuation of attacks. If they are not imminent, there are alternatives, and the use of force is not necessary.”

In short, the state acting in self-defense must show that it was necessary to use military force. Article 2(4) of the United Nations Charter prohibits states from resorting to force unless in self-defense or with Security Council authorization. The burden is on a state acting in self-defense to satisfy the test of necessity. (Yes, the use of force here was against non-state actor groups, not a sovereign state, but it was done in the territory of a nonconsenting sovereign state—Syria. Hence Article 2(4) applies.)

Recall that after the Trump administration’s targeted killing of General Soleimani, the administration claimed that the strike was justified as an act of self-defense. This argument was widely criticized, including by me. There was no evidence that, in fact, an attack was imminent and that, even if it was, killing Soleimani would make such an attack less likely.

We need to apply the same standard here: Is there sufficient evidence that the groups the Biden administration targeted were planning an attack and that the actions taken were necessary (and proportional) to stopping those attacks.

Here, one question is whether a past pattern of conduct is sufficient. Is it enough that “these groups” have participated in past attacks on the United States and have offered no sign of a change of heart? As Monica Hakimi framed the issue, because “we can’t know whether future attacks will occur, the is whether we should take a series of past attacks as good enough evidence that they will recur to satisfy the necessity criterion.” The analysis is complicated by the somewhat odd decision of the administration to frequently refer to the targets of its response as “Iran-supported non-state militia groups” rather than by name. There are, unfortunately, a lot of “Iran-supported non-state militia groups.” (The DOD statement is more precise, explaining that the facilities destroyed in Syria were “used by a number of Iranian-backed militant groups, including Kait’ib Hezbollah (KH) and Kait’ib Sayyid al-Shuhada (KSS).”) It would clearly be impermissible to respond against one or more Iran-supported groups because another Iran-supported group has a past pattern of attacks (unless, perhaps, the groups are each considered “organs” of Iran, as defined in Article 4 of the Draft Articles on the Responsibility of States for Internationally Wrongful Acts; that, however, would raise its own legal issues, including whether the strikes then need to be considered strikes on Iran itself). But assuming we’re talking about the same non-state group (or groups), are past attacks enough?

It is true that past attacks increase our confidence that a future attack may take place. But there are two reasons to be skeptical of this line of argument. First, self-defense is an exception to a general rule (a rule that, I have argued, is the foundational principle of the international legal order), and any efforts at expansion should therefore be read narrowly. A heavy burden, in other words, is on those seeking to expand the exception. Second, attacks that have been completed in the past don’t tell us that a use of force against a group is necessary to prevent future threats. We still need to ask whether there are alternative means to prevent the attacks.

The War Powers Report and Article 51 letter may get us out of having to resolve this difficult question, as they both hint at evidence that these groups were planning future attacks. The War Powers Report says that “these groups are also engaged in ongoing planning for future such attacks.” The Article 51 letter similarly claimed that the targeted facilities were used “by Iran-supported non-State militia groups that are responsible for recent attacks against U.S. personnel and are engaged in ongoing planning for future such attacks.” Thus, the Administration is not resting its argument that it was acting in self-defense on the past pattern of attacks alone. Neither statement provides any specifics, perhaps understandably. But those specifics are essential to evaluating the legality of the U.S. operation. Often, this is where we end up in assessing legality: The administration makes vague claims that may require classified evidence to assess, which puts those of us watching from the outside in a poor position to assess whether the strike was legal.

Fortunately, members of Congress are in a much better position to raise these very issues, and they should. They should examine, moreover, what the Administration means by “planning for future such attacks.” Past attacks combined with vague future planning is not sufficient to meet the necessity standard. Instead, there would need to be evidence that the groups were preparing for imminent attacks, not some possible attacks at some point in the future that they may or may not carry out.

One also cannot help but wonder why these groups were attacked in Syria if they pose a threat to U.S. forces in Iraq. Why not attack the groups in Iraq, where they pose the threat? After all, the U.S. military is operating in Iraq with permission of the Iraqi government, so taking action against these groups could potentially be done even without requiring a self-defense justification. (Consent to the use of force means that there is no Article 2(4) violation to which an exception is required.)

The Wall Street Journal has reported that the attack took place in Syria rather than Iraq to avoid undermining Iraqi Prime Minister Mustafa al-Kadhimi, who “would likely have faced criticism at home if the attacks had occurred on Iraqi territory.” If true, that raises some troubling questions. The Prime Minister would have faced criticism at home, presumably, because Iran-supported non-state groups have been formally incorporated into the Iraq armed forces as Popular Mobilization Forces. If that is the reason for avoiding taking the strikes in Iraq, that raises real questions about whether strikes against these groups in Syria were really “necessary” in the sense that there are no reasonable effective alternatives—including putting pressure on Iraq to reign in the militias itself.

Does the March 3 attack on Al Asad air base in Iraq strengthen or weaken the Administration’s argument?

On the one hand, it may seem that the March 3 attack strengthens the administration’s case that attacks by these groups (assuming they are the same groups) were being planned. After all, an attack has now happened! That would seem to suggest that attacks were, indeed, imminent.

But the fact that the attacks took place raises questions about efficacy and thus necessity of the strike against the groups in Syria. Even if the groups attacked the United States in the past and were planning attacks in the future, if the use of force against them did not prevent those attacks, then the use of force was, at least in hindsight, not necessary. It was not necessary because it did not, in fact, serve the intended aim: it did not prevent the attacks. Indeed, there is more than a small chance that the attacks were precipitated by our attack, just as the attacks on the same air base were likely precipitated by the killing of Soleimani in January 2020.

Stephen Pomper, Interim Chief of Policy at Crisis Group and former Special Assistant to the President and Senior Director for Multilateral Affairs and Human Rights at the National Security Council under President Obama, put this question pointedly: “I really wonder whether the USG thinks these strikes are going to be especially effective in addressing future risk.” To the extent that we appear to be allowing ourselves to get dragged into a tit-for-tat exchange of fire with these groups, it is hard to argue that the actions fit the requirements of self-defense. If the predictable result of our strike is that these groups will respond with a strike of their own—because even if we hit the right groups, they are diffuse and resilient enough not to be prevented from acting—our strike would seem to fail the necessity test. Indeed, Pentagon Press Secretary John Kirby acknowledged that the fact that the new attack came shortly after the U.S. response was a “troubling development.” But instead of accepting that it raised questions about the efficacy of strikes to deter the groups, he seemed to suggest the administration might double down: “if there is a need to further respond, we’re — we will do that, as I said, in a manner of our own choosing.”

The administration seems to be operating on the theory that it can make future attacks on U.S. troops and coalition forces less likely by sending the message to Iran that there will be costs imposed when Iran-backed groups attack our troops or coalition forces. But it’s far from clear that this approach has worked. Meanwhile, stretching and perhaps breaking international law has costs of its own, including increasing the chances that other states will follow in our footsteps, using force under dubious claims of self-defense.

What was the authority as a matter of domestic law?

Turning to domestic law, there are additional concerns—some of them related. Sens. Tim Kaine (D-Va.), Chris Murphy (D-Conn.) and Rep. Ro Khanna (D-Calif.) criticized the Biden administration for the airstrike and demanded that Congress immediately be briefed on the matter.

What was the stated basis under domestic law for the operation on Feb. 25? An NSC spokesperson stated that the president took the action “pursuant to his Article II authority to defend U.S. personnel.” The fact that the Administration issued a War Powers Report that does not reference any statutory authorities further indicates that it does not consider the operation to be covered by any existing statutory authority.

This is a more honest answer, I think, than we have sometimes seen. The 2002 Authorization for Use of Military force Against Iraq has previously been used to claim authority for actions in both Iraq and Syria. As I have argued elsewhere, any reasonable reading of that AUMF is that it has long since run its course. In 2014, the Obama administration advocated its repeal and said that it “is no longer used for any U.S. government activities.” That did not stop the Trump administration from suggesting it could support military operations, including the strike against Qassem Soleimani in Iraq in January 2020.

But while more intellectually honest, the Biden administration’s reliance on bare Article II authority is still deeply problematic. The U.S. personnel defense argument has expanded significantly over the years. The initial, not unreasonable, idea was that the president not only had the power to protect the United States, but U.S. citizens abroad as well. In 1992, for example, the Office of Legal Counsel justified the president’s decision to commit troops to secure the humanitarian assistance effort in Somalia in part on the basis of the president’s authority to protect the lives of Americans overseas—in that case persons involved in the humanitarian relief effort. It has since expanded to cover not only civilians but also members of the U.S. military, and now, apparently, contractors. In 2017, the Trump administration even tried to throw the U.S. force self-defense shield over the non-state partner forces of the Syrian Democratic Forces. Placement of U.S. forces in a conflict zone thus becomes the camel’s nose under the tent, inevitably giving rise to endless radiating additional claims of authority to use force in “self-defense” when those forces and those providing support or assistance to them inevitably come under threat. Indeed, Bill Barr once endorsed a radical “force protection” policy that would have justified a first strike to protect pre-positioned troops.

Even more troubling, if our strikes’ primary effect is to provoke a strike back—a strike on those very same forces we mean to be defending—then we run into the same problem as with the international law justification. Self-defense is not really self-defense if instead of preventing a threat, it precipitates it.

Where is the legal explanation from the Administration?

The Biden administration deserves real credit for quickly issuing both an unclassified War Powers Report and an Article 51 letter to the United Nations, which it also made public. But, like prior administrations, it has not released anything approaching a real legal justification for the strike.

That is a real problem.

Those of us on the outside are left to read the tea leaves and guess at the justifications. One step the Biden administration can and should take is to issue a more detailed unclassified legal memo explaining the justification for the strike. If it does not, Congress can and should insist on such an explanation—not just for this strike but for all future uses of force. (I lay out the case for this more fully in a recent article, “National Security lawyering in the Post-War Era: Can Law Constrain Power?”) The American people deserve at least a full explanation of the legal basis for deploying lethal force, especially if in doing so the government may be putting Americans in the region at future risk.

Finally, I will close by admitting to being saddened that we’re back here yet again. Again, we are having to try to parse the possibly dubious (and certainly unclear) legal justifications for yet another use of military force in the Middle East that seems once again to have little chance of making the situation in the region any better and might just make it worse.

Photo By: Air Force Staff Sgt. Jack Sanders, DOD