The news that Vance -- who led the last round of talks with Tehran in Islamabad, but came away with no deal -- would not travel this time emerged in a confusing manner, as members of Trump's cabinet had said he would in fact go.

"It's only because of security," Trump told ABC News, dismissing any notion that Vance was removed from the trip due to concerns about his ability to secure an agreement with the Islamic republic.

"JD's great," Trump added.

Washington's envoy to the United Nations, Mike Waltz, had told ABC News's "This Week" program: "As the president announced, the vice president with our key negotiators looks like they are going to head out for another round."

Energy Secretary Chris Wright told CNN's "State of the Union" that Vance had been "leading the negotiations from the start" though he did not explicitly say he would travel this time.

It was thus not clear who would lead the US team for talks expected to begin on Monday. Trump's special envoy Steve Witkoff and his son-in-law Jared Kushner were on hand last time around on April 11-12.

Earlier in a post on his Truth Social platform, Trump accused Iran of a "Total Violation" of the countries' two-week ceasefire with attacks Saturday in the Strait of Hormuz -- and threatened to destroy its power plants and bridges if no deal is reached.

Trump said he was offering Iran "a reasonable deal" and if Tehran refuses, "the United States is going to knock out every single Power Plant, and every single Bridge, in Iran. NO MORE MR. NICE GUY!"

"They'll come down fast, they'll come down easy and, if they dont take the DEAL, it will be my Honor to do what has to be done, which should have been done to Iran, by other Presidents, for the last 47 years," he wrote.

Waltz said he believed the new round of talks would lead to an "incredibly consequential" outcome.

The Strait of Hormuz remained closed on Sunday amidst the stand-off. Iran on Saturday declared it shut again to shipping -- one day after saying it would reopen the strategic waterway.

A UK maritime security agency said Iran's Revolutionary Guards had fired at one tanker on Saturday, while security intelligence firm Vanguard Tech reported the force had threatened to "destroy" an empty cruise ship that was fleeing the Gulf.

In the third incident, the UK agency said it received a report of a vessel "being hit by an unknown projectile, which caused damage" to shipping containers but no fire.

The US-Iran ceasefire is scheduled to end on Wednesday.