The Biden Administration’s Decision to Transfer Cluster Munitions to Ukraine: Legal and Policy Considerations

by | Jul 21, 2023

Cluster munitions

The Biden administration recently announced the approval of a new arms package for Ukraine that will, for the first time, include the provision of cluster munitions. This decision follows media reporting indicating that the administration had been “actively considering” whether to supply Ukraine with cluster munitions for some time.

The announcement is set against the backdrop of domestic legislation that prohibits military assistance in the form of cluster munitions unless the submunitions “do not result in more than 1 percent unexploded ordnance.” Since no cluster munitions in the current inventory meet that threshold, on its face the transfer appears to violate domestic law.

From an international law perspective, cluster munitions are widely denounced as “indiscriminate” and even “internationally banned” weapons. If these characterizations are accurate, the use of cluster munitions by Ukraine—and potentially even the provision of the weapons by the United States—would appear contrary to international law as well.

This post examines the central domestic policy and legal framework and the international law considerations involved with the Biden administration’s decision to transfer cluster munitions to Ukraine. I conclude that the supply and use of the weapons is consistent with the United States’ domestic and international legal obligations.

I have written a companion article that is posted on Lawfire as part of a mini-forum on the present topic that explores the issues of public perception, diplomatic implications, and congressional involvement related to the administration’s decision to supply cluster munitions to Ukraine. For present purposes, the substantive analysis begins by assessing provisions of domestic law and policy that are relevant to the transfer.

Domestic Law and Policy Pertaining to Cluster Munitions

The domestic legal and policy framework begins by tracing current Defense Department policy related to the use and transfer of cluster munitions. The current version replaced the policy published during the Bush administration in 2008 intended to gradually phase out stocks of cluster munitions that don’t meet the “1% unexploded ordnance” requirement.

This policy was not modified during the Obama presidency, though his administration did express in 2011 that the United States would “continue to implement its own voluntary policy to prohibit by 2018 the use of cluster munitions with more than a one percent unexploded ordnance rate.”

The Defense Department policy was then revised in 2017, early in the Trump administration, delegating to combatant commanders the “approval authority to employ cluster munitions that do not meet” the 1% unexploded ordnance threshold. This policy remains active during the Biden presidency, with no indication that the current administration is formally reviewing the Trump-era policy. During a press conference in March 2022, Pentagon Press Secretary John Kirby, while responding to a question from a journalist, indicated that he didn’t “have any updates…on the policy reviews with respect to cluster munitions.”

The existing 2017 policy prohibits the Defense Department from transferring cluster munitions to other countries “except as provided for under U.S. law.” The transition from the policy to the legal framework, then, begins with the Consolidated Appropriations Act of 2010, which prohibits the transfer of cluster munitions unless the submunitions, after arming, “do not result in more than 1 percent unexploded ordnance across the range of intended operational environments.” Subsequent versions of the appropriations act contain a similar provision, including the most recent legislation adopted for 2023.

Although the general rule prohibits the transfer of cluster munitions with a dud rate that exceeds the 1% threshold, The Foreign Assistance Act of 1961 (as amended through December 2022) provides an exception to the rule. According to Sec. 614 of the Act, the “President may authorize the furnishing of assistance” to a foreign government “without regard to” other relevant provisions of U.S. law—including appropriations legislation—when the President determines “that to do so is important to the security interests of the United States.”

Therefore, as long as President Biden assessed that providing cluster munitions to Ukraine is important to U.S. national security interests, current domestic law allows him to do so. I address additional potential concerns regarding the constitutionality of the restriction in the Consolidated Appropriations Act and the role of Congress in the debate regarding the provision of cluster munitions to foreign governments in my companion post on Lawfire.

International Law Pertaining to Cluster Munitions: Oslo Convention

Analysis related to the use and transfer of means of warfare such as cluster munitions pursuant to international law begins by determining whether a prohibition involving that particular weapon applies.

The United States is not allowed, for example, to use or transfer “laser weapons specifically designed…to cause permanent blindness to unenhanced vision” since the United States has ratified an international protocol with this prohibition. Likewise, the United States is not allowed to use or transfer chemical weapons, both because the government has ratified the Convention on Chemical Weapons and because it is uncontroversial to characterize the prohibition as a matter of customary international law.

The same is not true, however, regarding cluster munitions. The Convention on Cluster Munitions—often referred to as the “Oslo Convention”—does prohibit the use and transfer of cluster munitions. However, the United States has neither signed nor ratified this convention. In fact, the government refrained from participating in the “Oslo Process” that gave rise to the treaty.

Considering that only 110 countries have ratified the Oslo Convention and that customary international law is established by “extensive and virtually uniform” State practice that is performed out of a sense of legal obligation, the infrequent claim that the treaty itself constitutes customary international law is groundless. Because 74 countries have neither signed nor ratified the Oslo Convention (with another 13 that have signed but not ratified the treaty), and because non-ratifying countries such as the United States and Russia continue to possess and use cluster munitions, there is no legitimate claim that the provisions of the treaty reflect extensive and virtually uniform State practice.

This is why the frequent assertion that cluster munitions are “internationally banned” is a misnomer. Countries that have ratified the Oslo Convention are indeed “banned” from possessing, transferring, or using cluster munitions by virtue of the obligations they have assumed by agreeing to be bound by the text of the treaty. This does not mean the weapons themselves are internationally banned. Those countries that have not ratified the Convention remain free to possess, transfer, and use cluster munitions, and doing so is consistent with international law.

As such, neither conventional nor customary international law prohibits the United States from transferring cluster munitions to Ukraine. Neither country has ratified the Oslo Convention and the treaty itself does not constitute customary international law. That leaves the issue whether international law prohibits the use of cluster munitions even though the text of the Oslo Convention doesn’t apply in this instance.

International Law Pertaining to Cluster Munitions: Law of Armed Conflict

The starting point for the analysis of how international law in general applies to the use of cluster munitions is Additional Protocol I to the 1949 Geneva Conventions (AP I). Both Ukraine and Russia have ratified AP I, and the treaty applies to the current conflict pursuant to Article 1(3) of the treaty (which, in turn, refers to Common Article 2 to the 1949 Geneva Conventions). The United States has signed but not ratified AP I, though it does recognize relevant provisions of the treaty as customary.

The first relevant provision of the law of armed conflict (LOAC) reflected in AP I addressed here is the distinction rule. As AP I establishes, attacks (including those conducted with cluster munitions) “shall be limited strictly to military objectives” rather than civilian objects. If an attack is directed at a military objective but incidental damage to civilian persons or property is nonetheless anticipated, the proportionality rule must also be considered.

Although AP I does not directly use the term “proportionality,” the text prohibiting attacks that “may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated” is widely referred to as the proportionality rule. The United States considers the articulations of the distinction and proportionality rules reflected in AP I to represent customary international law.

Before moving on from the proportionality rule, two points should be noted.

First, the rule is sometimes characterized as preventing attacks that cause “damage or death [that is] ‘excessive’ in relation to the anticipated ‘concrete and direct military advantage’” resulting from the attack. This is a false interpretation of the rule in that it focuses on the outcome of a strike rather than the process that led to the attack. The “may be expected” clause that precedes the “incidental loss” provision of the rule as well as the “anticipated” clause that follows the “military advantage” portion confirm that the outcome of an attack is irrelevant when applying the proportionality rule.

Second, it is often suggested that reverberating effects must be considered when evaluating the proportionality rule. This interpretation represents an unwarranted attempt to develop a rule that is more constraining than international law actually requires. As the Department of Defense Law of War Manual (the “Manual”) notes on the subject, an attacker is “not be required to consider the possibility that a munition might not detonate as intended and might injure civilians much later after the attack.”

Harm that is anticipated from the actual attack is addressed by the plain text of the proportionality rule. Persistent efforts to expand the rule beyond the immediate anticipated harm to account for reverberating effects or remote harm constitute humanitarian overreach that is not supported by extensive and virtually uniform State practice that is performed out of a sense of legal obligation.

The requirement to take feasible precautions in the attack is also often cited when analyzing whether the use of cluster munitions complies with international law. However, as the Manual observes in relation to the feasible precautions requirement, determining “what precautions are feasible depends greatly on the context and other military considerations.”

This LOAC requirement, then, is not particularly useful when assessing the international law considerations involved in the decision whether to provide cluster munitions to Ukraine. It will be up to individual users of the weapons to implement feasible precautions in the attack based on the military considerations involved with each particular strike.

Are Cluster Munitions Prohibited by LOAC as “Indiscriminate” Weapons?

This leaves the LOAC discrimination rule left to consider. It is likely the most important factor since this is the rule that is most often cited to support the claim that the use of cluster munitions is unlawful under many circumstances.

The central components of the discrimination rule are established in Article 51(4) of AP I. The U.S. military applies this articulation from AP I in practice as an expression of customary international law. The most pertinent aspect of the discrimination rule prohibits attacks that “employ a method or means of combat the effects of which cannot be limited as required by this Protocol and consequently…are of a nature to strike military objectives and civilians or civilian objects without distinction” (emphasis added).

This rule is most often mischaracterized in the context of cluster munitions in one of two general ways.

One is to claim that cluster munitions are indiscriminate because the unexploded ordnance that is often left behind after an attack does not discriminate between opposing military forces and civilians. This is an incorrect interpretation of the relevant text of AP I. The actual rule addresses whether the means of warfare allows for the differentiation between military objectives and civilian objects during the strike—not days, weeks, months, or years later.

A second common misinterpretation of the LOAC discrimination rule involves a claim that cluster munitions cannot be used in populated areas since the effects of the actual strike ostensibly cannot be sufficiently limited. This, too, is incorrect. The “as required by this Protocol” provision that follows the “cannot be limited” component includes, among other provisions of AP I, the proportionality rule addressed above.

If a target is situated in a populated area and incidental damage is anticipated from the strike, those responsible for the attack will apply the proportionality rule whether unitary or cluster munitions are used. The wider collateral hazard area involved with cluster munitions will almost certainly result in more anticipated incidental damage and will thus affect the proportionality assessment.

As a matter of doctrine, however, the collateral hazard area can be identified for both categories of munition: unitary and cluster. As such, the effects of the attack can be limited and a proper proportionality assessment can be performed with both categories of munition “as required by” AP I when incidental damage is anticipated.

So, neither the transfer of cluster munitions from the United States nor the use of the weapons by Ukraine is prohibited pursuant to international law. This is not to suggest that all uses of cluster munitions would be automatically lawful, but compliance with international law would be a matter for those responsible for utilizing them on the battlefield.

Human Rights Law and the Transfer and Use of Cluster Munitions

One remaining aspect of international law to be addressed in the analysis is the extent to which, if at all, human rights law is implicated in the transfer and use of cluster munitions.

The issue of human rights was recently raised, for example, in a statement released by a coalition of nineteen progressive members of the House of Representatives denouncing the announcement that the Biden administration plans to transfer cluster munitions to Ukraine. In the statement, the group insists that supporting Ukraine in the fight against Russian aggression does not require the United States to undermine its “leadership in advocating for human rights around the world” and enabling “indiscriminate harm that will only further endanger Ukrainian civilians.”

Similarly, Representative Ilhan Omar (D-Minn.) reportedly asserted on the same topic, “If the U.S. is going to be a leader on international human rights, we must not participate in human rights abuses.” Likewise, Sera Koulabdara, CEO of the advocacy group Legacies of War, urged members of Congress “and other leaders to continue to stand on the side of the basic human rights to live free from the fear of cluster munitions and speak out publicly to their colleagues and the American people.”

With human rights law being relied upon so extensively to denounce the decision by the Biden administration and to generate political pressure in an effort to block or reverse the decision, it is worth assessing to what degree human rights law is a factor in the transfer and use of cluster munitions.

There is no human rights instrument that directly establishes a basic human right “to live free from the fear of cluster munitions,” and it is far from certain that human rights law in general plays any role in the transfer and use of cluster munitions. According to the U.S. government’s long-standing interpretation of the relationship between human rights law and LOAC, human rights do not factor in the discussion at all.

This is because, according to the U.S. view, “the law of war is the lex specialis during situations of armed conflict, and, as such, is the controlling body of law with regard to the conduct of hostilities and the protection of war victims.” There is no question that Ukraine is involved in an armed conflict with Russia and that LOAC applies to the conduct of hostilities.

If Ukraine employs cluster munitions against adversaries in the conflict, which will undoubtedly be the case, LOAC is the controlling legal framework rather than human rights. As such, it seems difficult to sustain the assertion that the decision to transfer cluster munitions to Ukraine will jeopardize American “leadership in advocating for human rights around the world” or will involve participating “in human rights abuses” in Ukraine.


This post has outlined the central legal and policy considerations that are relevant to the Biden administration’s recent announcement regarding the transfer of cluster munitions to Ukraine, from a domestic and international law perspective.

Pursuant to domestic law, the administration has statutory authority to provide security assistance—notwithstanding appropriations legislation that might otherwise block the transfer of cluster munitions—when the president determines that doing so is important to the security interests of the United States.

Because neither the United States nor Ukraine has ratified the Oslo Convention, the United States may transfer, and Ukraine may use, cluster munitions.

Ukrainian forces must still comply with relevant aspects of LOAC when using the weapons, but cluster munitions are neither inherently indiscriminate nor “internationally banned” in general as a matter of international law. Despite some examples of recent political and public rhetoric, LOAC—and not human rights—is the controlling body of international law against which the transfer and use of cluster munitions is to be evaluated.

There are undoubtedly policy and practical concerns associated with the transfer and use of cluster munitions, and perhaps even intense moral and ethical concerns as well. However, these prospective reservations should be distinguished from legal considerations. As a matter of law—both domestic and international—the transfer of cluster munitions from the United States and their use by Ukraine is consistent with relevant legal obligations.

Ukraine must still comply with international law on the battlefield when cluster munitions are utilized, but this will be the subject of a separate inquiry altogether.


Brian L. Cox is a doctoral candidate lecturer and J.S.D. candidate at Cornell Law School, a visiting scholar at the University of Ottawa Faculty of Law (Common Law Section) in Ontario, and a retired U.S. Army judge advocate.


Photo credit: U.S. Army via Wikimedia Commons