The Twelve-Day Iran–Israel War from the Perspective of International Law

Abstract

The recent military confrontations between the Islamic Republic of Iran and Israel, particularly Israel’s attack on Iran on 13 June 2025 and the subsequent twelve-day war, have once again highlighted the necessity of reassessing the legitimacy of the use of force under international law. The central question of this study is whether Israel’s reliance on the doctrine of “anticipatory self-defense” to justify its military operations, and Iran’s military response based on the inherent right of self-defense, can be legally justified within the framework of international law. Using a descriptive-analytical approach and drawing upon international legal instruments, judicial decisions, and legal doctrines, this study examines the legality of the military actions undertaken by both parties within the framework of the United Nations Charter and related legal doctrines. The analysis is organized around four major themes: (1) the theoretical and legal foundations of the use of force, (2) the historical and political context of Iran–Israel tensions, (3) the status of self-defense, anticipatory self-defense, and preventive self-defense in international law, and (4) the legal assessment of the military actions of both parties. The findings indicate that the doctrines of anticipatory and preventive self-defense, particularly in the absence of an imminent armed attack, lack a solid legal basis in contemporary international law. Consequently, Israel’s military operations may be characterized as a clear instance of aggression. In contrast, Iran’s military response to those attacks, provided that the five essential conditions of lawful self-defense—namely the occurrence of an armed attack, necessity, immediacy, proportionality, and notification to the United Nations Security Council-are satisfied, may be considered consistent with Article 51 of the United Nations Charter. The study concludes that the legality of military action can only be justified within the framework of peremptory norms and the established practice of international law. Expansive interpretations of Article 51 of the Charter constitute extra-legal readings that may serve as a justification for the use of force and pose a threat to the international legal order.