In the Russian-Ukrainian war, both sides use cluster ammunition. While Hungarian news outlets paid little attention to the fact that the Russian military, unlike the Ukrainian side, used such weapons extensively following the February 2022 escalation (already in the early days of the full-scale invasion), it was widely reported in July 2023 that the United States provided cluster munitions to Ukraine. This article attempts to explore the international legal aspects of this question, clarifying whether the warring parties and their supporters violate their international obligations by using and making cluster weapons available.
Cluster munition
Pursuant to the definition in Article 2 of the international convention prohibiting its use, “cluster munition means a conventional munition that is designed to disperse or release explosive submunitions each weighing less than 20 kilograms, and includes those explosive submunitions”. These munitions, also known as cluster bombs, can be launched from an aircraft, but also from land and water; they open up in the air and release the smaller bombs and submunitions that had been arranged in clusters inside them, thereby covering a large area. Persons staying in the impact zone of these tens or hundreds of exploding mini-bombs have minimal chance for surviving unharmed.
Convention on arms restriction and disarmament
Because cluster bombs take their victims indiscriminately and without distinguishing between legitimate military targets and peaceful civilian persons and property, and because some of their small charges do not explode during deployment and remain active and highly dangerous even long after the conflict, some countries decided in 2008 to introduce and undertake a ban on these weapons. Adopted in Dublin and opened for signature in Oslo some fifteen years ago, the convention on cluster munitions eventually entered into force in 2010 after it was ratified in the required number of countries.
Until the first half of 2023, 111 states agreed to undertake the obligations stipulated in the convention. As there are some 200 countries today, we are far from having the convention signed and ratified by all countries. However, all signatories (including Hungary) undertook “never under any circumstances to use cluster munitions; develop, produce, otherwise acquire, stockpile, retain or transfer to anyone, directly or indirectly, cluster munitions; assist, encourage or induce anyone to engage in any activity prohibited to a State Party under this Convention ”(Article 1).
Russia, Ukraine, or the USA has not signed this Convention. However, it is characteristic of international public law that the entities that create the law, i.e. the states, are also the entities that must follow it. In other words, an international treaty may not give rise to any right or obligation on the side of third parties (as a general rule, see Articles 34 to 37 of the 1969 Vienna Convention on the Law of Treaties). A state may decide for itself which obligations it undertakes and which it stays away from.
However, the sources of international law are by no means limited to treaties. Customary international law has always had and still has a prominent role in international law. This type of legal source forms part of the general rules of international law, and (also as a general rule) it binds all members (i.e. states) of the international community. So the question is: even if Russia and Ukraine (as well as the United States) have stayed away from the international convention banning cluster bombs, are they not bound by a norm of customary law? In other words, does this convention on arms restriction codify a rule of customary law? Does international customary law prohibit the use of cluster munitions? If the answer were yes, then it would be irrelevant whether all the states had ratified the Dublin Convention of 2008, as all states would still be subject to a legal obligation, but on a different legal ground, namely customary law (see Article 38 of the 1969 Vienna Convention).
Norms of international customary law
It is difficult to give a definite answer to the above questions because of the uncertainty inherent in customary international law (see points 136 to 137, 146, 162, 167, 177 in the textbook by János Bruhács). Nevertheless, the driving force of international humanitarian law, i.e. the International Committee of the Red Cross (ICRC), can provide us some guidance. In 2005, the Red Cross summarized in an in-depth monograph (available here and here, and also published in a continuously updated online database) what it considers norms of humanitarian law, i.e. those rules for the protection of victims of armed conflicts that form part of customary law and that are binding for all warring parties regardless of their assumed contractual obligations.
As for the use of cluster bombs, the 161 rules of customary law, identified by the ICRC, do not include any explicit prohibition. With regard to, for example, biological weapons (rule 73), chemical weapons (rule 74), and expanding bullets (rule 77), The Red Cross determined that the use of such weapons is banned under customary law both international and non-international armed conflicts. (Points 72 to 86 cover all rules of customary law identified in relation to weapons.) Does it follow from the above considerations that a state is not obliged to refrain from using cluster bombs unless it has agreed to be bound by the Dublin Convention of 2008? Not at all!
For the time being, the Red Cross does not consider that a total ban on cluster bombs has been established as a norm of customary international law, as the two conditions of establishing such norms have not been met (i.e. an existing general practice among states, and that practice having been accepted as law). However, this does not mean that the use of such weapons by states that reject the Dublin Convention is necessarily legal.
The most important guiding aspects are presented below following the reasoning of William H. Boothby:
1) Warring parties that are not parties to the Dublin Convention are also prohibited from using cluster bombs, namely on the basis of customary law, if this munition cannot be directed at a given target, or its effect cannot be limited to a given target, and, by its nature, it indiscriminately hits both military targets and civilian persons and property. This is true because launching indiscriminate attacks is prohibited under customary law (rule 11).
2) It is also prohibited for belligerents not party to the Dublin Convention to use cluster bombs, also on the basis of customary law, if, as a result of the use of this munition, the remaining unexploded charges cause civilian casualties, deaths and injuries to such an extent that the weapon, in terms of its effect, is also considered indiscriminate. This is true because the use of weapons which are by nature indiscriminate is prohibited by customary law (rule 71).
3) Even if it is possible to specifically direct a given cluster munition to a military target, and it is not considered to be indiscriminate by nature, it is still forbidden for warring parties that are not parties to the Dublin Convention to use that weapon, also on the basis of customary law, without taking into account, for example when planning an attack, the extent of collateral damage caused to civilian lives and/or property in addition to the expected military advantage, or without obtaining all available information for such calculations. This is true because, under customary law, each party to the conflict must take all feasible precautions in the choice of means and methods of warfare with a view to avoiding, and in any event to minimizing, incidental loss of civilian life, injury to civilians and damage to civilian objects (rule 17), and each party to the conflict must do everything feasible to assess whether the attack may be expected to cause incidental civilian casualties which would be excessive in relation to the concrete and direct military advantage anticipated (rule 18).
4) After taking account of the norms of customary law, it should finally be emphasized that both Russia and Ukraine are signatories to the Protocol on Explosive Remnants of War to the Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons which may be deemed to be Excessively Injurious or to have Indiscriminate Effects (Protocol V), adopted by 97 states in 2003 and in effect since 2006, which requires the removal and destruction of such remnants, and the cleaning of the affected areas. This obligation applies also to submunitions that fall from cluster bombs but fail to explode.
About anti-personnel mines as an analogy
In order to better understand the difference between a clear prohibition under a treaty (binding only the parties to the convention) and the sometimes more uncertain obligation under customary law (applicable to all states), it is worth examining the international regulation of anti-personnel mines. (Regarding nuclear weapons, see this analysis by the author.)
A convention on the prohibition of anti-personnel mines was adopted in 1997 and it has been signed by 164 states. The parties to the convention adopted in Oslo and opened for signature in Ottawa have undertaken never under any circumstances to use anti-personnel mines; to develop, produce, otherwise acquire, stockpile, retain or transfer to anyone, directly or indirectly, anti-personnel mines; or to assist, encourage or induce, in any way, anyone to engage in any activity prohibited under the convention (Article 1).
The vast majority of the international community accepted these obligations, but some thirty states decided to stay away from the convention. However, their freedom is also limited, as they are bound by the norms of customary law. The experts of the International Committee of the Red Cross believe that, for the time being, there has not yet been a comprehensive customary law ban similar to that laid down in the convention in relation to anti-personnel mines. Nonetheless, the ICRC considers it proven that today all states are obliged under customary law to at least the followings: 1) When using anti-personnel mines, special care must be taken to minimize their indiscriminate effect. (This means that there is no customary law ban on their use, but, for example, they can only be deployed to protect military objects, and minefields must be carefully marked, drawing the attention of the population to the danger.) 2) In close relation to the previous consideration, the belligerent party using mines must, as far as possible, record the location of anti-personnel mines. 3) Finally, every state participating in an armed conflict is obliged, after the hostilities have ended, to remove any anti-personnel mines it has deployed, or otherwise to ensure that the population is not endangered by the mines (i.e. neutralize the mines). (Points 81 to 83).
It seems from the above that the customary law prohibition falls short of the much stricter contractual obligation. However, customary law is not a static source of law. The practice of states and the associated legal convictions may develop in such a way that the customary law prohibition, which is binding for all states, becomes identical to the provisions of the convention on disarmament. This is the case, for example, of chemical weapons. While the treaty on the prohibition of such weapons (opened for signature in 1993) has become almost universal, it has be ratified by 193 states until this day. Nevertheless, the stigmatizing effect of the convention banning cluster bombs may lead to a change in the practices of states, even if this optimistic scenario may not be the first to come to mind in the context of the Ukrainian-Russian war. Still, it is worth noting that, since the adoption of the treaty, the USA, for example, has only once carried out an isolated cluster bomb attack in Yemen in 2009, their production was stopped in 2008, and the Biden administration also proceeded with utmost care and circumspection when such weapons were handed over to Ukraine.
Conclusion
It follows from the above considerations that, even if the existence of a universally binding ban on cluster munitions seems uncertain, using cluster munition in a way that violates other clear norms of customary law is certainly considered a war crime. (It is also clear that the US, which is not a party to the convention, did not violate its international obligations by handing over such weapons.)
It is a war crime, for example, to use such weapons against otherwise legitimate military targets that are located in densely populated cities, as they cause disproportionate collateral damage. It is a war crime to use such weapons against dual-purpose facilities (i.e. facilities used both for military and civilian purposes), such as railway stations without taking into account that civilians fleeing from the fights might fall victim to the attack. It is also a war crime, of course, to destroy residential areas and housing estates using such weapons, whether the attacker acts intentionally or negligently.
Even if there is some uncertainty regarding the obligations of states that have not accepted the convention on cluster munitions, the fundaments is clearer than ever: with its aggression against Ukraine, Russia not “only” violates its contractual obligations declared in the UN Charter, but it also disregards the universally binding rules, known as ius cogens, of international law by ignoring the universal prohibition of violence. There are no war crimes without starting a war. From the perspective of ius ad bellum (the right to war) (i.e. regarding the rules on the use of force between states), the Russian Federation violates the law; from the perspective of ius in bello (i.e. regarding the norms governing an armed conflict that has already started), both warring parties may commit a violation if they ignore humanitarian international law, including the contractual and customary rules on the use of weapons.
Picture by: U.S. Army / Wikipedia
