The European Peace Facility (EPF) is a new mechanism officially established to allow the EU to directly assist partners in military and defence matters. After the Russian Federation’s invasion of Ukraine, the Council of European Union adopted assistance measures under the EPF financing equipment and supplies for the Ukrainian armed forces, including, for the first time, the provision of lethal equipment. This article firstly presents the legality and compliance of this provision with the law of neutrality under international law on the assumption that providing military support to a state unlawfully attacked might represent a mitigating circumstance – considering the inherent right to self-defence – and a collective countermeasure in response to severe violations of collective obligations. Then, the article discusses international responsibilities arising in case of violations of international law committed with EU-provided weapons: not only Ukraine would be liable, but also the EU and its Member States (MS) could be co-responsible for not having adequately assessed the misuse of the weapons or their diversion. Indeed, the accountability framework would appear tripartite and divided between Ukraine, the recipient state, the EU, the formal sender, and its Member States, who fund the assistance measure through an off-budget fund.