The Multifaceted Criminal Notion of Terrorism in International Law

Posted: 18 Jun 2008

Date Written: November 2006


Contrary to what many believe, a generally accepted definition of terrorism as an international crime in time of peace does exist. This definition has evolved in the international community at the level of customary law. However, there is still disagreement over whether the definition may also be applied in time of armed conflict, the issue in dispute being in particular whether acts performed by freedom fighters in wars of national liberation may (or should) constitute an exception to the definition. As a consequence of disagreement on terrorism in armed conflict, states have so far been unable to lay down a general definition of the whole phenomenon of terrorism in a general treaty. The fact, however, remains that under current customary international rules terrorism occurring in a time of peace and which is international in nature (i.e. not limited to the territory of a state and showing transnational connections) may, depending on the circumstances, constitute a discrete international crime, or a crime against humanity. In time of armed conflict, terrorism (i.e. attacks on persons not taking an active part in armed hostilities, with a view to spreading terror among the civilian population) currently amounts to a specific war crime (crime of terror). In time of armed conflict, terrorist acts may also amount to crimes against humanity (if part of a widespread or systematic attack on the civilian population). The objective and subjective elements of each of these three classes of criminal conduct are set out in the article on the basis of existing international law. While in the view of the author, the current legal regulation of terrorism is thus sufficiently clear, the fact remains that states are politically and ideologically divided on whether the actions of freedoms fighters involving attacks on civilians should be defined as terrorist or instead lawful. In this contentious area three divergent political trends are emerging in the world community: (i) to sic et simpliciter exempt freedom fighters actions from the category of terrorism, without however specifying what law would regulate their actions or whether such actions are in any case always lawful; (ii) to exclude attacks against civilians in armed conflict from the legal regulation of the international rules on terrorism and thus assign such legal regulation to international humanitarian law solely; (iii) to combine the application of both international norms on terrorism and international humanitarian law to actions in armed conflict, classifying as terrorist (not as war crimes) attacks on civilians carried out in the course of such conflicts with a view to spreading fear.

Suggested Citation

Cassese, Antonio, The Multifaceted Criminal Notion of Terrorism in International Law (November 2006). Journal of International Criminal Justice, Vol. 4, Issue 5, pp. 933-958, 2006, Available at SSRN: or

Antonio Cassese (Contact Author)

University of Florence ( email )

Piazza di San Marco, 4
Florence, 50121

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