Iranian President Masoud Pezeshkian has described U.S. President Donald Trump’s threat to send Iran “back to the Stone Age” as an indication of possible large-scale war crimes. According to Al Jazeera, Pezeshkian said such statements reveal an intent to cause massive destruction, which could be considered a serious violation of international law.

Referring to his discussion with Finnish President Alexander Stubb, Pezeshkian noted that he had raised the issue with his Finnish counterpart, who is a legal expert. He added that history contains many examples where silence in the face of crimes has come at a great cost.

The remarks come amid heightened tensions following reports of a U.S. acknowledgment of an Iranian warplane being shot down and warnings that any attack on Iran’s power facilities would constitute a war crime.