Washington DC - President Donald Trump said he was postponing a planned attack on Iran scheduled for Tuesday at the request of Gulf leaders amid "serious negotiations" with Tehran.

Trump's sudden announcement on social media on Monday came after Iran said it had responded to a new US proposal aimed at ending the war.

Trump said he would "hold off on our planned Military attack of the Islamic Republic of Iran, which was scheduled for tomorrow," in a message on his Truth Social network.

The US president said he had been asked to do so by the leaders of Qatar, Saudi Arabia, and the United Arab Emirates as "serious negotiations are now taking place."

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The Gulf allies believe "a Deal will be made" that includes "NO NUCLEAR WEAPONS FOR IRAN!" added Trump.

Trump said he had informed the US military "that we will NOT be doing the scheduled attack of Iran tomorrow."

But he said he had "further instructed them to be prepared to go forward with a full, large-scale assault of Iran, on a moment's notice, in the event that an acceptable Deal is not reached."

Trump had given Iran a series of increasingly ominous warnings in the days since his return from a trip to China to meet President Xi Jinping.

Late Sunday, he said the "clock is ticking" and threatened that "there won't be anything left" of Iran if no peace deal is reached.

The US and Israel have been locked in a war with Iran since US and Israeli forces launched strikes in late February.

Trump has struggled to break an impasse in negotiations and end the conflict, which has shaken the Middle East and sent energy prices climbing.

The two sides have held only a single round of talks in Pakistan despite a fragile ceasefire in April.

On Sunday, Iran's Fars news agency said Washington had presented a five-point list, which included a demand for Iran to keep only one nuclear site in operation and transfer its stockpile of highly enriched uranium to the US.

Fars said that the Iranian proposal had emphasized that Tehran would continue to manage the strategic Strait of Hormuz, a vital energy conduit which Iran has largely kept closed since the start of the war.

On Monday, the Persian Gulf Strait Authority (PGSA), a new body Iran has set up to manage the Hormuz Strait, said it would provide "real-time updates" on X of operations and developments in the waterway.

Trump says Iran must open up the strait as part of any deal.