International law governing war or self-defense allows countries to knowingly kill some civilians as an incidental consequence of attacking a legitimate military target, so long as the bystander deaths are deemed necessary and proportionate. But some international law scholars, European allies and human rights groups disagree with the United States’ position that war zone rules — like a right to attack militants based only on their status as enemy fighters, even if they do not pose a literally imminent threat at that moment — apply to counterterrorism strikes outside conventional battlefields.