Training the RSF? Due Diligence, Unlawful Intervention, and Criminal Exposure in Sudan’s War

[Girmay Tesfakiros Meressa holds an LL.M. in International Operational Law and is a legal practitioner. His research interests include the law on the use of force, international humanitarian law, and international criminal law, with a particular interest in the legal regulation of contemporary armed conflicts]

Introduction

A recent investigation by Reuters alleges that Ethiopia constructed a secret facility used to train fighters belonging to Sudan’s Rapid Support Forces (RSF), one of the principal belligerents in the ongoing armed conflict in Sudan. Shortly after the report, Sudan accused Ethiopia of involvement in its civil war. If accurate, these allegations raise legal questions: when does external support to a non-state armed group cross the line from geopolitical maneuvering into an internationally wrongful act?

This post briefly examines the principal legal dimensions of the alleged conduct, focusing on due diligence obligations of states, the prohibition of unlawful intervention and indirect uses of force, and the potential criminal exposure that may arise where external support contributes to the commission of international crimes.

Due Diligence and the Duty to Prevent

International law requires states to ensure that their territory is not knowingly used for acts that harm the rights of other states. Even before the prohibitions on intervention or the use of force are triggered, the allegations reported by Reuters implicate the due diligence obligations of states.

This principle was famously articulated by the International Court of Justice in the Corfu Channel Case, where the Court held that states must not knowingly allow their territory to be used for acts contrary to the rights of other states. At a minimum, this obligation requires a state to take reasonable steps to prevent harmful activities once it becomes aware of them.

Allowing armed groups engaged in a conflict in another state to organize, recruit, or train on one’s territory may therefore engage the responsibility of the territorial state for failing to exercise due diligence. Such a situation would amount to an omission: a failure to prevent harmful acts emanating from a state’s territory.

However, the allegations reported by Reuters go further. The reported construction of a training facility and the organized training of fighters would not merely represent a failure to prevent harmful conduct. Rather, it would suggest active facilitation of an armed actor engaged in an ongoing conflict in Sudan.

If substantiated, such conduct may therefore move beyond a breach of due diligence and enter the realm of prohibited intervention under international law.

Unlawful Intervention and the Use of Force

The principle of non-intervention prohibits coercive interference in matters within another state’s sovereign domain. In its landmark judgment in Military and Paramilitary Activities in and against Nicaragua, the International Court of Justice made clear that providing training, logistical support, or assistance to armed groups operating against another state may constitute unlawful intervention.

Importantly, not every form of support automatically amounts to a prohibited use of force under Article 2(4) of the United Nations Charter. The Court distinguished between unlawful intervention and the more serious violation of the prohibition of force.

Training fighters alone will often fall into the former category. Yet the line is not rigid. Where support becomes extensive—through large-scale training, operational coordination, or deep military integration—the conduct may approach, or even cross, the threshold of a prohibited use of force.

This distinction is central to assessing the legal consequences of alleged Ethiopian support to the Rapid Support Forces in Sudan. Even absent direct battlefield control, structured military training provided to an armed group fighting a foreign government may fall within the scope of prohibited intervention.

Even if structured military training were to cross the threshold into a prohibited use of force, the further question arises whether it would amount to an “armed attack” within the meaning of Article 51 of the Charter of the United Nations. In Military and Paramilitary Activities in and against Nicaragua, the International Court of Justice distinguished between the “most grave forms” of the use of force, which qualify as armed attacks, and less grave violations that do not trigger the inherent right of self-defence.

The provision of training, logistical support, or operational assistance—absent direct participation in hostilities or the sending of armed bands of sufficient scale—may therefore fall below the armed-attack threshold. In such circumstances, the injured state’s response would generally be confined to lawful countermeasures, diplomatic protest, or recourse to international dispute settlement mechanisms, rather than forcible self-defence.

Armed Attack and Self-Defence

The jurisprudence of the International Court of Justice draws an important distinction between the “most grave forms of the use of force,” which qualify as armed attacks, and less grave violations that do not trigger the right of self-defence. In Military and Paramilitary Activities in and against Nicaragua, the Court suggested that providing training or logistical assistance to armed groups generally falls below the armed-attack threshold.

If the allegations against Ethiopia concern only the construction of a training camp and the training of fighters belonging to the Rapid Support Forces, the legal response available to Sudan would therefore likely lie not in the use of force but in diplomatic protest and the adoption of non-forcible countermeasures.

That said, the scale and context of the support remain legally significant. Systematic military training provided to an armed group actively engaged in an ongoing armed conflict could amount to substantial involvement in the hostilities. Such conduct might bring the activity closer to the prohibition of the use of force under Article 2(4) of the Charter of the United Nations.

Even in that scenario, however, the availability of self-defence under Article 51 would remain uncertain. Crossing the Article 2(4) threshold does not automatically amount to an armed attack. Unless the support reaches the level of the “most grave forms” of force identified in Military and Paramilitary Activities in and against Nicaragua, forcible self-defence may not yet be legally justified.

Internationalization of the Conflict

External support to one of the parties may also raise the question whether the conflict could become internationalized. Under international jurisprudence, such a transformation generally requires a high degree of control by the supporting state over the armed group.

In Prosecutor v. Tadić, the International Criminal Tribunal for the Former Yugoslavia articulated the “overall control” test for determining when the actions of a non-state armed group may be attributed to a foreign state for the purposes of classifying a conflict. Under this approach, a conflict may become internationalized if a supporting state not only assists an armed group but also organizes, coordinates, or directs its military operations.

Training fighters or providing logistical assistance, without operational or strategic control over the group’s battlefield conduct, is unlikely on its own to satisfy this threshold. Nevertheless, if a supporting state becomes sufficiently involved in shaping the group’s military activities, the legal characterization of the conflict may change.

The consequences would be significant. The supporting state could be regarded as a party to the conflict, and the legal framework governing the hostilities would shift accordingly. Full international armed conflict rules under Geneva Conventions and customary international humanitarian law would apply. In that sense, the question of external support illustrates the point at which jus ad bellum considerations intersect with the classification of conflicts under international humanitarian law.

International Humanitarian Law Implications

The training of fighters participating in an armed conflict also carries implications under international humanitarian law. When individuals are trained and equipped for participation in hostilities in a context where serious violations of humanitarian law are widely reported, such assistance risks facilitating further abuses. While international humanitarian law primarily regulates the conduct of parties during hostilities, external actors that enhance the operational capacity of armed groups may indirectly contribute to patterns of violations.

The relevance of due diligence obligations in this context has been emphasized in the jurisprudence of the International Court of Justice, particularly in the judgment in Application of the Convention on the Prevention and Punishment of the Crime of Genocide (Bosnia and Herzegovina v. Serbia and Montenegro). In that case, the Court clarified that states may incur responsibility not only for directly committing internationally wrongful acts, but also for failing to take reasonable measures to prevent international crimes where there is a serious risk that they may occur.

This reasoning suggests that, where external assistance significantly strengthens the military capacity of actors operating in environments marked by widespread humanitarian law violations, questions may arise as to whether the supporting state has exercised the level of vigilance required under international law. In that sense, the due diligence framework also provides a conceptual bridge between the law governing state responsibility and the potential relevance of international criminal law in situations where serious violations are alleged.

Individual Criminal Responsibility

The legal implications do not end with questions of inter-state responsibility. The allegations also raise potential issues of individual criminal liability under international criminal law. If the supported armed group commits war crimes or crimes against humanity, the conduct of individuals who knowingly assist those operations may fall within the scope of international criminal law.

Under The Rome Statute of the International Criminal Court,  individuals may incur criminal responsibility not only for directly committing international crimes but also for aiding and abetting their commission. Article 25(3)(c) provides that a person may be criminally responsible where they provide assistance, encouragement, or other support that has a substantial effect on the commission of a crime, with awareness that their conduct facilitates the criminal activity.

In this context, providing training, resources, or organizational support to armed actors may qualify as such assistance if it materially strengthens the capacity of a force engaged in the commission of international crimes. Where officials or other actors knowingly train or equip a group that is committing atrocities, the training itself could constitute a form of practical assistance that substantially contributes to those crimes.

Given the numerous allegations of serious abuses, individuals involved in organizing or facilitating military training for armed groups could therefore face scrutiny if their actions materially contribute to the commission of such crimes.

Conclusion

If the reported training of Rapid Support Forces fighters on the territory of Ethiopia is confirmed, the allegations raise serious concerns under international law. At a minimum, such conduct may implicate a breach of due diligence obligations and the prohibition of unlawful intervention in the affairs of Sudan.

The legal consequences, however, may extend further. What begins as a failure to prevent harmful activities emanating from a state’s territory may escalate into unlawful intervention, potentially approach the prohibition of the use of force under the Charter of the United Nations, and—where the supporting state exercises sufficient involvement—contribute to the internationalization of the conflict.

The implications do not end with inter-state responsibility. If the supported armed group commits war crimes or crimes against humanity, individuals who knowingly assist those operations may face scrutiny under international criminal law.

Support to armed groups in contemporary conflicts therefore activates multiple layers of legal responsibility. The consequences extend beyond diplomatic friction, engaging foundational principles of non-intervention, state responsibility, and potentially individual criminal liability.

Photo Attribution: “Western Deffufa” by Walter Callens is licensed under CC BY 2.0