U.S. President Donald Trump on Thursday threatened to destroy Iran’s bridges and power plants, saying the “New Regime leadership knows what has to be done, and has to be done, FAST!” in a Truth Social post.

Trump did not elaborate on what needed to be “done,” but said the U.S. “hasn’t even started destroying what’s left in Iran.”

Hours later, Iran’s semi-official Tasnim news agency reportedly claimed that a U.S. F-35 fighter jet was shot down over central Iran. Images of the jet were posted on Telegram, with one photo that appeared to show the words “U.S. Air Forces in Europe” on what appeared to be the tail section of a plane.

The U.S. Central Command, which oversees the region, and Iranian authorities did not respond to a request for comment at the time of publication.

Trump’s latest threat came a day after a nationwide address in which he said the U.S. military would hit Iran “extremely hard” for the next two or three weeks. He added that the U.S. would “bring them back to the Stone Ages where they belong.”