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This glossary contains key terms relating to counterterrorism under international law. There is no unified definition of terrorism in international law. Different definitions exist depending on whether the terrorist act is committed in peacetime or in connection with an armed conflict.

Last updated: one year ago


Accountability concerns the responsibility of individual law enforcement officials, law enforcement agencies, and States for potentially unlawful use of force. Accountability is required by international law and both legal and practical measures must exist domestically.


In accordance with the official commentary to Article 1 of the 1979 Code of Conduct for Law Enforcement Officials, “the term ‘law enforcement officials’ includes all officers of the law, whether appointed or elected, who exercise police powers, especially the powers of arrest or detention”.  Law enforcement officials include the military, “whether uniformed or not”, as well as other State security forces, wherever they exercise such powers. 


The term ‘less-lethal’ is not formally defined under international law, but is generally understood to designate a wide array of weapons whose ordinary use typically results in death less often than do firearms; Less-lethal weapons range from the traditional police baton to encompass pepper spray, tear gas, conducted electrical weapons such as Tasers®, flash-bang grenades, rubber and plastic bullets, water cannon, acoustic weapons, and malodorants.


The principle of necessity holds that police and other law enforcement officials may only use minimum necessary force for a legitimate law enforcement purpose. Once the need for any force has passed, application of further force will thus be unlawful. 


The principle of precaution requires that the authorities plan law enforcement operations in a manner that minimises the risk of the police having resort to a potentially lethal weapon and thereby to lessen the possibility of death or serious injury to a member of the public or law enforcement official. 


The principle of proportionality sets an upper limit on when minimum necessary force may be lawful, based on the threat posed to life or limb and/or to property.


As set out in Basic Principle 9 of the 1990 Basic Principles on the Use of Force and Firearms, firearms may be used by law enforcement officials when it is necesssary to do so in self-defence or defence of others against the imminent threat of death or serious injury. While death may result from the use of firearms, this should not normally be the intent. 


As set out in Basic Principle 9 of the 1990 Basic Principles on the Use of Force and Firearms, intentional lethal use of firearms (i.e. shooting with intent to kill) "may only be made when strictly unavoidable in order to protect life".