In recent years, the international community has witnessed the emergence of a terrorist group called ISIL (Da’esh) or "Islamic State in Iraq and the Levant" and its terrorism in various parts of the world especially the Middle East, which has severely endangered international peace and security through their violent acts. The terrorist acts and international crimes of ISIL prompt an inquiry into applicability of international law to such nonـstate actors. Also despite the various measures taken to combat ISIL, the prosecution, trial and punishment of members of this terrorist group have not been fulfilled yet. This article by examining the main areas of international law and some of the legal and political obstacles concludes that the existing international law does not adequately address the activities of ISIL, and the failure of the international community to execution of criminal justice to ISIL members and leaders reveals that a new international mechanism and more cooperation between states are needed.
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