“There seems to be little doubt that spreading terror among Iranian civilians is the primary purpose of Trump’s threat,” Heller noted. “That said, Trump’s threat is unlikely to qualify as a war crime,” he added, noting that international tribunals have typically required such threats to result in “grave consequences” for civilians — and “that has obviously not happened yet.”
Others suggest such rhetoric may be unlawful under international law without necessarily meeting the threshold for a war crime.
“These threats violate the prohibition against giving no quarter,” said Gerry Simpson, professor of public international law at the London School of Economics, referring to a rule in the laws of war, codified in Additional Protocol I to the Geneva Conventions, that forbids declaring that no enemy fighters will be spared or that surrender will not be accepted.
“This is obviously cruel and dangerous — and possibly deranged,” Simpson told POLITICO. “But it also constitutes an act under international law and one with legal effect.”
At the heart of the debate is a distinction that international law draws, sometimes awkwardly, between what is unlawful and what is criminal.
International law clearly prohibits threats of force, including under the U.N. Charter’s ban on “the threat or use of force” against other states. But turning such threats into war crimes typically requires a higher bar, with international tribunals focusing on conduct that produces concrete effects, as reflected in case law from tribunals such as the International Criminal Tribunal for the former Yugoslavia’s Prosecutor v. Dragomir Milošević.