Attacking the Quds Force and Affiliated Groups under the Jus ad Bellum
On 28 January, a drone strike on a U.S. military outpost in Jordan known as Tower 22 killed three soldiers and wounded 34. The Islamic Resistance in Iraq, a non-State militia group, claimed responsibility for the attack which it said was in response to U.S. support for Israel in its fight against Hamas. The same day, U.S. President Biden blamed “radical Iran-backed militant groups operating in Syria and Iraq” and declared, “[W]e will hold all those responsible to account at a time and in a manner our choosing.”
That accounting began on 2 February. As U.S. Central Command announced,
U.S. Central Command (CENTCOM) forces conducted airstrikes in Iraq and Syria against Iran’s Islamic Revolutionary Guards Corps (IRGC) Quds Force and affiliated militia groups. U.S. military forces struck more than 85 targets, with numerous aircraft to include long-range bombers [B-1] flown from the United States. The airstrikes employed more than 125 precision munitions. The facilities that were struck included command and control operations centers, intelligence centers, rockets, missiles, unmanned aerial vehicle storage, and logistics and munition supply chain facilities of militia groups and their IRGC sponsors who facilitated attacks against U.S. and Coalition forces.
According to National Security Council spokesperson John Kirby, the “targets were carefully selected to avoid civilian casualties and based on clear, irrefutable evidence that they were connected to attacks on U.S. personnel in the region.” The strikes are just the beginning, for President Biden has stated that the operations “will continue at times and places of our choosing.” He warned, “Let all those who might seek to do us harm know this: If you harm an American, we will respond.” It is important to point out that although this was the first attack in which U.S. military personnel died, there have been over 160 attacks in Syria and Iraq since the Hamas attack on Israel on 7 October. The United States has struck back at the militia groups that conducted them on multiple occasions, most recently on 23 January.
Putting aside the question of whether the operations and the manner in which they are being conducted make strategic and operational sense (I believe they do), this post examines whether the strikes and those that are likely to follow comply with the jus ad bellum, the law governing the resort to force by States (on the strikes against the Houthis and the jus ad bellum, see Buchan). I caution readers that the jus ad bellum is a body of law brimming with interpretive disagreement among States and scholars (see, e.g., Arimatsu/Schmitt on attacking ISIS). Therefore, although I will offer my views, I will also highlight the relevant points of contention.
Law versus Motivation
There are only two universally accepted bases for the use of force by a State: authorization by the United Nations Security Council under Chapter VII of the UN Charter; and self-defense pursuant to Article 51 and customary international law. Because the Security Council did not authorize the U.S. strikes, self-defense is the only possible legal basis for conducting them.
As is evident in the text of Article 51, a State’s use of force must be in response to an “armed attack.” Furthermore, State practice and opinio juris confirm that the response must be both “necessary” and “proportionate,” requirements examined below that the International Court of Justice (ICJ) has cited repeatedly (e.g., Paramilitary Activities, para. 194; Nuclear Weapons, para. 41; Oil Platforms, para. 76).
The necessity criterion concerns whether forcible action is needed to repel an imminent or ongoing armed attack; if non-forcible measures would suffice, the victim State’s right to act forcibly in self-defense has not matured. Proportionality, by contrast, is about how much force may be used by a State to defend itself effectively. Employing more than required would constitute a wrongful use of force in violation of Article 2(4) of the UN Charter and customary international law. As a practical matter, the ambiguity in these standards allows States a fair margin of appreciation.
In this case, U.S. officials and spokespersons have repeatedly talked in terms that suggest a U.S. response would be in retaliation for the previous strikes. Indeed, even the mainstream media has frequently cited retaliation as the motive for the U.S. response (e.g., here, here, and here). However, retaliation (or revenge, vengeance, etc.) is never a legal basis for using force or any other response under international law (e.g., countermeasures under the law of State responsibility). A State’s actions may be motivated in part by a desire to strike back, but forcible action must be firmly grounded in a valid need to use force to defend against an armed attack.
The same is true concerning deterrence. For instance, Lindsay Graham, a powerful U.S. Senator in national security affairs, has argued, “The only thing the Iranian regime understands is force. Until they pay a price with their infrastructure and their personnel, the attacks on U.S. troops will continue.” He may be right, and the U.S. response was undoubtedly motivated by a justifiable desire to deter continued Iranian support for the militia groups and future attacks by them on U.S. forces. But the legal justification for the U.S. response must be found in the law of self-defense.
The only time a State may use force to preclude future attacks is when those attacks are imminent, as the term is understood in the law governing “anticipatory self-defense” (Greenwood, Max Plank Encyclopedias of International Law, paras. 41-51), or an armed attack campaign is underway, and the goal is to deter its continuation (see below). In other words, it is permissible to strike targets to degrade the adversary’s capability for launching or continuing an armed attack, but it is not lawful to do so solely to deter the possibility of future attacks. Deterrence may be a consequence of lawful self-defense, but it does not legally justify acting defensively.
Lastly, punishment is not a legal basis for a State’s use of force. Thus, holding accountable those responsible for the attacks, as threatened by President Biden, provides no legal basis for the U.S. strikes. This does not mean they may not be killed during operations that comply with the conditions for self-defense. Indeed, in some cases, directly targeting them may be the most effective means of self-defense, as when the individuals are planning, approving, or executing the armed attacks.
The point is that while nothing is unlawful about a State’s forcible operation being motivated by a desire to retaliate, deter, or punish, none of those objectives provides any legal basis for using force. This being so, I turn to the conditions for the exercise of the right of self-defense.
Armed Attack
The attacks against the U.S. forces raise two issues concerning whether they qualify as an armed attack, triggering the right of self-defense. The first concerns the severity of the action to which a defensive use of force responds. The prevailing view, expressed by the ICJ in its Paramilitary Activities (Nicaragua) judgment, is that “armed attacks” are the “most grave form” of a use of force, a term used in Article 2(4) of the UN Charter’s prohibition on using force (para. 191). The United States takes a different approach by which all uses of force qualify as an “armed attack” under Article 51 and the international customary law of self-defense (Department of Defense (DoD), Law of War Manual, § 1.11.5.2).
This difference in interpretation has, in my estimation, little bearing on the characterization of the attack on the Tower 22 outpost. It is surely the case that a forcible action that kills three and wounds 34 soldiers crosses the armed attack threshold, irrespective of whether that threshold is higher than that which applies in the use of force prohibition.
The second issue deals with identifying the entity responsible as a matter of law for engaging in the armed attack. To begin with, since the attacks of 9/11, a debate has raged over whether the right of self-defense extends to attacks by non-State groups. The United States has argued that it does, correctly in my opinion, as have many other States, NATO, and international law experts (DoD, Law of War Manual, § 1.11.5.4; Schmitt, p. 104-06). Indeed, five days before the Tower 22 attack, the United States launched airstrikes against “militia groups affiliated with Iran’s Islamic Revolutionary Guard Corps,” including Kata’ib Hezbollah, in response to attacks on U.S. and coalition personnel at Al-Asad airbase in Iraq. In its Article 51 notification letter to the UN Security Council (a requirement of Article 51), the United States stated that it had acted pursuant to its “inherent right of self-defense.”
It is difficult to see how States could respond otherwise to non-State attacks that are of a severity that would unequivocally qualify as armed attacks if mounted by States. But others disagree (see Haque’s survey and Hakimi’s discussion). The ICJ’s Armed Activities judgment (para. 146) and Wall advisory opinion (para. 139) bolster their position.
This is not the place to resolve the debate, but it is certainly a relevant one given that some of the U.S. strikes targeted assets of non-State groups. By the U.S. approach, self-defense would be available against those groups involved in at least the 28 January attack. It would also open the door to attacking any other militia groups operating in concert with the group that conducted it.
The problematic piece to the legal puzzle deals with the extent to which the groups the United States struck have been operating together since the October 7 attacks on Israel (the common motivation). If they were attacking the U.S. assets without collaborating or coordinating their operations, then attacks by each group would have to be assessed separately against the armed attack threshold, even if launched with the same motivation. Of course, by the U.S. approach that equates the use of force and armed attack thresholds, most would qualify as armed attacks against which the United States could respond forcibly, subject to the necessity and proportionality conditions. But by the alternative approach, which sees the armed attack as a higher threshold of severity, some groups’ attacks (e.g., a single unsuccessful mortar attack) might not qualify, thereby rendering forcible operations against the group concerned unlawful.
But if groups are collaborating or coordinating their operations, as the claim of responsibility by the so-called Islamic Resistance in Iraq would seem to suggest, all of them would be targetable in self-defense even if some had not mounted previous attacks reaching the threshold. Moreover, their attacks, even though not individually crossing the armed attack threshold, could be aggregated to the 28 January attack (on aggregation, see NATO Strategic Concept, para. 25). This would put the nail in the coffin of any assertion that the attacks against the United States were of insufficient severity to trigger the right of self-defense.
A remaining question involves the targeting of the Iranian Quds Force. Unless the Quds Force actions could independently qualify as an “armed attack,” forcible action against that organization could only be justified if the non-State groups’ attacks are attributable to Iran under international law. As noted in the UN General Assembly’s Definition of Aggression resolution (annex, art. 3(g)), which the ICJ adopted in its Paramilitary Activities judgment, this requires that the attacks be conducted “on behalf” of Iran or with its “substantial involvement” (para. 195). Substantial involvement is a somewhat ambiguous standard, but it is not satisfied by “the provision of weapons or logistical or other support.” According to the ICJ, such support may constitute a wrongful use of force or intervention but not an armed attack (Paramilitary Activities, para. 195).
However, if Iran was substantially involved in the 28 January attack (and the earlier ones), its Quds Force, an “organ” of the State, may be targeted by the United States, so long as this is necessary and proportionate. The situation would be treated as if Iranian forces had conducted the attacks themselves. Iranian substantial involvement would also open the door to a necessary and proportionate response against the non-State groups working with Iran, even for those States and scholars who would limit the use of force to armed attacks by States.
In this regard, note that the United States had previously taken action against the Quds Force, most prominently by killing its leader, General Qassem Soleimani, in 2020 on the basis that he was developing plans to attack U.S. forces and assets and had orchestrated previous attacks. More recently, the strikes that preceded the 28 January response also targeted Quds Force assets.
Iran has denied any involvement in the current round of attacks against U.S. forces. A spokesperson for the Foreign Ministry stated after the 28 January attack that the Iraqi militias “do not take orders” from Iran, acted independently, and that assertions to the contrary were “baseless.” Nevertheless, Iran has long-supported militia groups through the so-called “Axis of Resistance” and has even threatened Israel with its use to open new fronts in the war with Hamas.
Thus, whether the attacks can be attributed to Iran under the law of self-defense is fact-dependent. If they cannot, self-defense does not justify the attacks against the Quds Force. If they can, the Quds Force and other Iranian assets, as well as groups it is working with, may be attacked in self-defense by the United States, subject to the conditions of necessity and proportionality.
Necessity
The necessity criterion requires that “no reasonable alternative means of redress are available” other than a use of force (DoD, Law of War Manual, § 1.11.1.3). It was doubtful that non-forcible measures such as negotiations with the militia groups or Iran would have proven successful in putting an end to attacks on U.S. forces. This being so, that aspect of the necessity criterion was satisfied at the time of the US strikes.
A further question is whether the United States had a right to conduct the strikes nearly a week after the Tower 22 attack. The use of force in self-defense is only permissible in anticipation of an imminent armed attack or during an ongoing one (DoD, Law of War Manual, § 1.11.5.1); using force after an armed attack is over is mere retaliation. An overly rigid application of this limitation could render the U.S. strikes unlawful because of the lapse of time.
However, the law of self-defense must be interpreted in accordance with its object and purpose, which is to allow States to effectively defend themselves. In the case of a single attack that is unlikely to be repeated, the right of self-defense does terminate soon thereafter; arguments that the right of self-defense survives throughout the time necessary to prepare to conduct a response, standing alone, do not hold water.
But this was not an isolated attack, and indeed, not the first time the United States had struck facilities used by the IRGC Quds Force and affiliated groups following the October 7 Hamas attack on Israel (see U.S. Article 51 notification letters of 30 October; 14 November; 28 November; 26 January). These groups are plainly engaged in a campaign against U.S. assets in the region, and there is little reason to believe the attacks are going to stop, at least as long as Israel is engaged with Hamas and Islamic Jihad in Gaza. Indeed, the United States anticipated as much following the 23 January strikes when it noted that it would “take further such action in the region as may be necessary in the exercise of its inherent right of self-defence to respond to future attacks or threats of attacks against United States nationals and United States personnel and facilities.” And so it did on 2 February.
Therefore, the attacks launched before the U.S. strikes must be seen as taking place during an ongoing campaign against the United States. In the face of such a campaign, a State must be entitled to degrade and defeat its adversary’s ability to mount subsequent attacks. If this were not the case, the law of self-defense would be a defensive revolving door that would prove operationally unmanageable.
Proportionality
A similar logic applies when considering the proportionality criterion, which requires that no more force than needed be used to repel an armed attack (as distinct from the international humanitarian law rule of proportionality that deals with civilian harm). The DoD Law of War Manual explains that “assessing the proportionality of measures taken in self-defense may involve considerations of whether an actual or imminent attack is part of an ongoing pattern of attacks” (§ 1.11.1.2). To the extent attacks against U.S. forces continue, strikes preceding them cannot, by definition, be disproportionate. In this regard, the Institute for the Study of War has reported that “IRGC-controlled and local Syrian media claimed that the Islamic Resistance in Iraq conducted four drone and rocket attacks targeting US forces in Iraq and Syria on February 3,” the day after the U.S. strikes. Although the attacks are unconfirmed at the time this post is being drafted, the claims alone are a signal that the U.S. strikes have not put an end to militia attacks. And according to National Security Advisor Jake Sullivan, the United States intends to continue its defensive operations against them.
That said, there are indications that the U.S. operations are having some effect. For instance, the leader of Iran’s Revolutionary Guard stated in the aftermath of the 2 February U.S. strikes that his country was “not looking for war,” although it would respond if attacked. Additionally, Kata’ib Hezbollah, which may have been the group that carried out the 28 January attack, announced that it was suspending its operations in Iraq due to pressure from the Iraqi government. Nevertheless, until the U.S. operations prove successful, the United States retains its right to conduct forcible operations against the groups involved.
Location
The U.S. strikes into Iraqi and Syrian territory occurred without the consent of either country. Both have condemned them as violating their territorial sovereignty (see here, here, and here).
The nonconsensual penetration by one State of another’s territory indeed implicates the sovereignty rights of the latter. The question is whether the former’s right of self-defense can serve as a “circumstance precluding the wrongfulness” (Articles on State Responsibility, ch. V) of what would otherwise be a sovereignty violation (in this regard, see Buchan, arguing, correctly in my view, that self-defense is a circumstance precluding wrongfulness for non-forcible acts).
There are two views. According to the first, the sovereignty of a State that is not responsible for the armed attack is an impenetrable veil that may only be violated when the Security Council has authorized the action under Chapter VII or, perhaps (see Arimatsu/Schmitt, Necessity, p. 1193-94), in situations of “necessity,” as outlined in Article 25 of the Articles on State Responsibility. The Security Council has not acted, and in my opinion, the plea of necessity does not serve as a circumstance precluding the wrongfulness of the use of force. Therefore, by this first view, the U.S. operations in Syria and Iraq were “internationally wrongful acts.”
A second view has matured in the aftermath of the 9/11 attacks. Supported by the United States, numerous other countries, and many international law experts, it holds that the veil of sovereignty may be pierced by a State acting in legitimate self-defense. Known as the unwilling or unable approach, it balances two State rights: territorial sovereignty; and the right of self-defense. I have long supported the position, summarizing my views here.
It is essential to understand that the right of self-defense in such cases is limited. It arises only when the territorial State has been allowed to take action to end the misuse of its territory and cannot or will not do so. This condition is satisfied in the current situation, for neither State has taken effective action against the militia groups. Moreover, the approach does not countenance using force against the territorial State’s forces or assets unless it forcibly interferes with the exercise of the right of self-defense. The only hint in open source material that the United States may have done so is a report that it struck Iraq’s Popular Mobilization Forces (PMF). The Iraqi Prime Minister formally commands the PMF, but, in fact, the elements that were struck likely report to the IRGC Quds Forces. Thus, the limitation would not seem to apply to attacks on these forces.
Concluding Thoughts
The U.S. strikes that have been conducted against the Quds Force and affiliated non-State militia groups since Hamas’s October 7 attack on Israel may be motivated by a desire to retaliate, deter, or punish, but their legal justification may only reside in the right of self-defense. In that regard, numerous factual questions persist in publicly available sources, such as the Quds Force’s degree of involvement in the attacks and the relationship between the various groups making up the Islamic Resistance in Iraq.
Additionally, although I believe the U.S. positions on various disputed elements of the law of self-defense are sound, I recognize that reasonable minds differ on some of them, like the unwilling and unable doctrine. Nevertheless, in my estimation, the strikes are, as explained above, lawful responses to an ongoing armed attack campaign against U.S. forces in the region. Therefore, whether the United States continues to act in self-defense against these and future attacks in the ongoing campaign it faces is a matter of policy, not law.
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Michael N. Schmitt is the G. Norman Lieber Distinguished Scholar at the United States Military Academy at West Point. He is also Professor of Public International Law at the University of Reading and Professor Emeritus and Charles H. Stockton Distinguished Scholar-in-Residence at the United States Naval War College.
Photo credit: Senior Airman Matthew Bruch
