The United Nations Basic Principles for the Use of Force and Firearms by Law Enforcement Officials (UN Basic Principles) set out the international legal standard for the use of force by police:
Law enforcement officials shall not use firearms against persons except in
self-defense or defense of others against the imminent threat of death or
serious injury, to prevent the perpetration of a particularly serious crime
involving grave threat to life, to arrest a person presenting such a danger
and resisting their authority, or to prevent his or her escape, and only when
less extreme means are insufficient to achieve these objectives. In any
event, intentional lethal use of firearms may only be made when strictly
unavoidable in order to protect life.4
The United States has failed to follow these rules by using combat drones in places where no actual armed conflict was occurring or where the U.S. was not involved in the armed conflict.
Lawful Use of Combat Drones, Mary Ellen O’Connell