EN
The right of self-defense in response to an armed attack by a non-state actor is considered as one of the most interesting and controversial issues of contemporary international law. It may be argued that this issue has replaced other important and so far widely debated topics concerning the use of force, such as humanitarian intervention. What these issues have in common is undoubtedly an important element in the philosophy of international law and the triad of values: sovereignty, human rights, justice. The right of self-defense in response to an armed attack by a non-state actor affects not only the classical ius ad bellum issues, but also relations between customary and treaty norms, the principles of attributing responsibility to a state, and the concept of positive obligations. The importance of this topic has been revealed in the context of efforts of international community for an adequate response to armed attack by terrorist organizations, especially Al. Qaida at the turn of the century and, recently, the so-called Islamic State of Iraq and the Levant (hereinafter ISIL or Daesz). The issue of the right of self-defense in response to attack by a non-state actor is not explicitly regulated in the Charter of the United Nations. For this reason, a critical approach to this type of practice was prevalent throughout the Cold War period. Significant changes in the positions of states have begun in the second half of the 1990s, and an important precedent in this respect were actions in response to the attacks of September 11, 2001. In view of the skeptical stance of the International Court of Justice in its Advisory opinion of 2004, a possible change in approach in this respect can be derived from the practice of combating ISIL since 2014 and UN Security Council Resolution No. 2249. These actions, according to many commentators, seem to lead to the conclusion that international customary law, which is an integral part inherent in the right of self-defense, has evolved towards the recognition of the right of self-defense in response to the aggression of a non-state actor.