Trump's announcement came after he had threatened that the clock was ticking for Iran to strike an agreement or fighting would renew after a fragile ceasefire.
The president did not offer details about the planned attack he said was scheduled for Tuesday but said but he instructed the US military "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 not previously disclosed that he was planning a strike for Tuesday but over the weekend he warned, "For Iran, the Clock is Ticking, and they better get moving, FAST, or there won't be anything left of them".
Trump has been threatening for weeks that the ceasefire struck in mid-April could end if Iran did not strike a deal, with shifting parameters for striking such an agreement.
Trump said in his social media post that he was calling off the planned strike at the request of allies in the Middle East, including the leaders of Qatar, Saudi Arabia and the United Arab Emirates.
Trump has repeatedly set deadlines for Iran and then backed off.
Trump in recent days has also spoken with Israeli Prime Minister Benjamin Netanyahu and Chinese President Xi Jinping about the Iran war.
Earlier on Monday, a senior Iranian official told Reuters that the US had softened its position on some issues after Iran sent it a new peace proposal.
Pakistan, which has conveyed messages between the sides in the war in the Middle East since hosting the only round of peace talks last month, had shared the latest proposal with US, a source said.
The sides "keep changing their goalposts," the Pakistani source said, adding: "We don't have much time."
Iranian Foreign Ministry spokesman Esmaeil Baghaei confirmed that Iran's views had been "conveyed to the American side through Pakistan" but gave no details.
with AP
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