"Hopefully Iran will quickly 'Come to the Table' and negotiate a fair and equitable deal - NO NUCLEAR WEAPONS -- one that is good for all parties. Time is running out," the US leader said in a social media post, noting that "a massive armada is heading to Iran."

"As I told Iran once before, MAKE A DEAL! They didn't, and there was 'Operation Midnight Hammer,' a major destruction of Iran. The next attack will be far worse!"

The dialing up of threats came after Iran's top diplomat said the country would not come to the table under the shadow of military action.

"Conducting diplomacy through military threat cannot be effective or useful," Foreign Minister Abbas Araghchi said in televised comments on Wednesday. "If they want negotiations to take shape, they must certainly set aside threats, excessive demands and raising illogical issues."

Trump has repeatedly left open the option of new military action against Iran after Washington backed and joined Israel's 12-day war in June aimed at degrading Iranian nuclear and ballistic missile programs.

Earlier this month, he threatened to strike Iran over its deadly crackdown on anti-government protests. But the prospect of immediate American action seemed to recede in recent days, with both sides insisting on giving diplomacy a chance.

With a US naval strike group led by an aircraft carrier lurking in the region, top Iranian officials also reached out to key Arab states in behind-the-scenes diplomacy to rally support.

A strike group led by the USS Abraham Lincoln has now arrived in Middle Eastern waters, US Central Command said, without revealing its precise location.