Abstract This paper argues that, while the famous “first shot formula” represents the dominant interpretation for the application of common Article 2(1) of the Geneva Conventions, its application in the case of unilateral use of lethal force for the targeted killing of military personnel in the territory of a third state is not compatible with the requirements of humanity and the object and purpose of these treaties. The paper contends such an operation will not ipso facto trigger an international armed conflict between targeting state and the state of the targeted person. By examining the elements that constitute an international armed conflict, the paper proposes a new criterion for determining the beginning of such a conflict in cases of targeted killing of military personnel in the territory of a third state.