Iranian state media says that Iran has sent an official response to a letter from U.S. President Donald Trump to the Iranian supreme leader that was seen as an attempt to jumpstart talks over Tehran’s nuclear program.

Trump said that Iran faces severe consequences if it fails to reach a nuclear deal, after Tehran responded to a letter from the US president calling for talks.

President Donald Trump issued a stark warning to Iran on Friday, saying that unless Tehran agrees to a new nuclear deal with the United States, “very bad things” will happen to the country. The comments mark a sharp escalation in rhetoric as the two countries edge closer to a potential confrontation over Iran’s rapidly advancing nuclear program.