Iran and the United States traded threats on Wednesday after some of the heaviest fighting in weeks engulfed the Middle East, deepening the foes' stalemate six months into the war.

President Donald Trump said US forces staged a "very heavy attack" on Iranian targets overnight and are "prepared to do another one any time we want".

Tehran's security chief warned that Iran had adopted a "new strategy" in the war that began in late February with US-Israeli attacks on the Islamic Republic.

"You will soon see that Iran's new strategy on the battlefield, in diplomacy and in confronting the economic blockade will shatter your foundations," Supreme National Security Council Secretary Mohsen Rezaei wrote on X.

Washington has vowed to ramp up economic pressure on Iran, threatening its allies with sanctions.