President Donald Trump has said the US will inflict "TREMENDOUS Economic Consequences" on any country that helps or does business with Iran.
He wrote in all capital letters on Truth Social that he was launching "the most crushing economic operation ever taken against any country!" He gave no further details, and did not name any other nation.
It comes after a 60-day ceasefire with Iran expired on Monday, with no sign of a diplomatic or military off-ramp to the conflict that the US and Israel began at the end of February.
Trump's latest move appears to extend the pressure campaign of Operation Economic Fury, launched in April to sanction foreign banks or firms that do business with Tehran.
In Wednesday evening's social media post, Trump said he was launching "economic D-Day" on Iran because the Islamic Republic had failed to make a deal with the US.