The right to self-defence in Article 51 of the United Nations Charter is increasingly being invoked in response to armed attacks conducted by armed groups located in a territory of another state, with or without the (direct) assistance of such a state. This article examines the implications of the invocation of the right to self-defence under these circumstances for the principles of attribution within the jus ad bellum paradigm. First, it illuminates how the threshold requirements for indirect armed attacks (that is, the state acting through a private actor) have been lowered since the 1986 Nicaragua decision of the International Court of Justice. In so doing, the article suggests that in order to prevent a complete erosion of the benchmarks of an indirect armed attack, the notions of ‘substantial involvement’ in an armed attack, ‘harbouring’, and ‘unwillingness’ should be interpreted as manifestations of due diligence. Thereafter, the article illustrates that there is also an increasing attribution of armed attacks directly to non-state actors, notably those located in areas over which territorial states have lost control. Such states could be depicted as being ‘unable’ to counter the activities of non-state actors. The article further submits that particularly in these instances, the principle of necessity within the self-defence paradigm can play an important role in curbing the potential for abuse inherent in the vague notion of ‘inability’, if interpreted in light of Article 25 of the Articles on State Responsibility for Internationally Wrongful Acts.