This article examines whether general international law supports the claim that direct military assistance by one State to another State upon the latter's request is prohibited where the inviting State is implicated in (gross) violations of international humanitarian and/or human rights law. It approaches the question from the perspective of State responsibility, analysing the threshold requirements of Article 16 of the Articles on State Responsibility (ASR),1 which represents the customary international law standard for responsibility for aiding or assisting wrongful conduct by another State. In so doing, the article illuminates how factual uncertainties complicate the triggering of the responsibility of the intervening (assisting) State for any violations of international humanitarian and/or human rights law by the territorial (recipient) State. Thereafter, the article questions whether, in the event that the responsibility of the intervening State is triggered, it would in consequence have to withdraw its troops and/or military air power from the territorial State.