US President Donald Trump said on Monday he had called off a planned US military strike on Iran scheduled for Tuesday, citing a "very good chance" of reaching a deal to end the war.

In a post on Truth Social, Trump said Gulf allies, including Qatar, Saudi Arabia and the United Arab Emirates, had urged Washington to delay the attack because of progress in negotiations with Iran.

He added that the US military has been instructed to remain prepared for a "full, large scale assault" if talks fail.

"There seems to be a very good chance that they can work something out," Trump told reporters at the White House. "If we can do that without bombing the hell out of them, I'd be very happy."

Earlier, the US president had declared the fragile six-week ceasefire as being "on life support."