Iran and the United States agreed on Saturday to task experts to start drawing up a framework for a potential nuclear deal, Iran's foreign minister said, after a second round of talks following President Donald Trump's threat of military action.

At their second indirect meeting in a week, Foreign Minister Abbas Araqchi negotiated for almost four hours in Rome with Trump's Middle East envoy Steve Witkoff, through an Omani official who shuttled messages between them.

Trump, who abandoned a 2015 nuclear pact between Tehran and world powers during his first term in 2018, has threatened to attack Iran unless it reaches a new deal swiftly that would prevent it from developing a nuclear weapon.

Iran, which says its nuclear programme is peaceful, says it is willing to discuss limited curbs to its atomic work in return for lifting international sanctions.

Speaking on state TV after the talks, Araqchi described them as useful and conducted in a constructive atmosphere.

"We were able to make some progress on a number of principles and goals, and ultimately reached a better understanding," he said.

"It was agreed that negotiations will continue and move into the next phase, in which expert-level meetings will begin on Wednesday in Oman. The experts will have the opportunity to start designing a framework for an agreement."

The top negotiators would meet again in Oman next Saturday to "review the experts’ work and assess how closely it aligns with the principles of a potential agreement,” he added.

Echoing cautious comments last week from Supreme Leader Ali Khamenei, he added: "We cannot say for certain that we are optimistic. We are acting very cautiously. There is no reason either to be overly pessimistic."

There was no immediate comment from the US side following the talks. Trump told reporters on Friday: "I'm for stopping Iran, very simply, from having a nuclear weapon. They can't have a nuclear weapon. I want Iran to be great and prosperous and terrific."

Washington's ally Israel, which opposed the 2015 agreement with Iran that Trump abandoned in 2018, has not ruled out an attack on Iran's nuclear facilities in the coming months, according to an Israeli official and two other people familiar with the matter.

Since 2019, Iran has breached and far surpassed the 2015 deal's limits on its uranium enrichment, producing stocks far above what the West says is necessary for a civilian energy programme.

A senior Iranian official, who described Iran's negotiating position on condition of anonymity on Friday, listed its red lines as never agreeing to dismantle its uranium-enriching centrifuges, halt enrichment altogether or reduce its enriched uranium stockpile below levels agreed in the 2015 deal.