Abstract

Developing jus ad bellum outside the United Nations Charter (UNC) has met serious criticisms and challenges among lawyers and even in the practice of international tribunals; however, it has to be borne in mind that international lawyers are not solely Charter experts, on the contrary, we are bound to consider all the material sources of international law together and not necessarily under sometimes-impossibility of Charter provisions. In line with this argument, while some writers refute the very existence of the right for states to act in self defense against Armed Non State Actors (ANSA), referring to the International Court of Justice advisory opinion in 2004 that expressed the exclusivity of article 51 of the United Nations Charter (UNC) to the situations of state-state armed conflicts, This article concludes for permissibility of such a plea. For this, it will draw a distinction between international customary and international conventional law on the issue of self defense and then puts forward its supporting legal and material evidences in form of scrutiny of states' practice and the judicial records of the ICJ to prove the existence of opinio Juris supporting the customary right of states to self defense against ANSAs.