In his news conference Monday, Donald Trump threatened to blow up every bridge and power plant in Iran, action that would be so far-reaching that some experts in military law said it could constitute a war crime.

The issue could turn on whether the power plants were legitimate military targets, whether the attacks were proportional compared with what Iran has done and whether civilian casualties were minimized.

Trump’s threat was so broad it did not seem to account for the harm to civilians, prompting Democrats in Congress, some United Nations officials and scholars in military law to say such strikes would violate international law.