This paper examines the criticisms towards the use of unmanned aerial systems (UAS) to attack terrorist targets outside traditional “combat zones,” like Afghanistan and Iraq. The United States is not engaged in an armed conflict with al-Qaeda or any other militant group. Terrorist attacks are criminal acts that must be addressed with law enforcement measures, not armed attacks that give rise to the use of military force in self-defense. The use of force in this context is governed by international human rights law (IHRL), not international humanitarian law (IHL). Because armed drones are warfighting, not law enforcement, tools, they may not be used to strike terrorist targets outside the combat zone. Targeting individual terrorist leaders constitutes an unlawful extrajudicial killing in violation of IHRL. Conducting UAS strikes against terrorist targets within the territory of another nation without the consent of that nation violates Article 2(4) of the UN Charter. Even if the right of self-defense applies, the use of UAS to attack terrorist targets outside Afghanistan and Iraq violates the IHL principles of military necessity, proportionality and distinction. If the United States is engaged in an armed conflict, civilian UAS operators are unlawful combatants and may not participate in hostilities. UAS strikes may only be conducted against civilians who have taken a direct part in hostilities. Although acts of terrorism may cause harm, most do not meet the criteria for direct participation in hostilities. State responses to these acts must conform to the lethal force standards applicable to self-defense and law enforcement. The use of advanced weapons systems in lethal operations against terrorists is illegal under international law.