Trump, who will visit three other Gulf Arab monarchies next week, has voiced hope for reaching a deal with Tehran to avert an Israeli military strike on Iran's nuclear program that could ignite a wider war.

Three previous rounds of talks in Oman and Rome ended with notes of optimism, with the two sides saying the atmosphere was friendly despite the countries' four decades of enmity.

But they are not believed to have gone into technical detail, and basic questions remain.

Steve Witkoff, Trump's friend who has served as his globe-trotting negotiator on issues including on Iran, had initially suggested flexibility on Tehran maintaining low-level enrichment of uranium for civilian purposes.

But in an interview published Friday, Witkoff gave his clearest message yet that the Trump administration would oppose any enrichment.

"An enrichment program can never exist in the state of Iran ever again. That's our red line. No enrichment," he told right-wing Breitbart News.

"That means dismantlement, it means no weaponization, and it means that Natanz, Fordow and Isfahan -- those are their three enrichment facilities -- have to be dismantled," he said.

US Secretary of State Marco Rubio earlier raised the possibility of Iran importing enriched uranium for any civilian energy.

Trump in his first term withdrew from a nuclear agreement with Tehran negotiated by former president Barack Obama that allowed Iran to enrich uranium at levels well below what is needed for weapons.

Many Iran watchers doubted that Iran would ever voluntarily dismantle its entire nuclear program and give up all enrichment.

But Iran has found itself in a weaker place over the past year. Israel has decimated Hezbollah, the Lebanese Shiite militia backed by Iran that could launch a counter-attack in any war, and Iran's main ally in the Arab world, Syria's Bashar al-Assad, was toppled in December.

Israel also struck Iranian air defenses as the two countries came openly to blows in the aftermath of the October 7, 2023 attack on Israel by Hamas, which is also supported by Iran's clerical state.

- 'Blow 'em up nicely' -

Trump himself has acknowledged tensions in his policy on Iran, saying at the start of his second term that hawkish advisors were pushing him to step up pressure reluctantly.

In an interview Thursday, Trump said he wanted "total verification" that Iran's contested nuclear work is shut down but through diplomacy.

"I'd much rather make a deal" than see military action, Trump told the conservative radio talk show host Hugh Hewitt.

"There are only two alternatives -- blow 'em up nicely or blow 'em up viciously," Trump said.

Iranian Foreign Minister Abbas Araghchi said that Oman, which has been mediating, had proposed Sunday as the date and both sides had accepted.

"Negotiations are moving ahead and naturally, the more we advance, the more consultations we have, and the more time the delegations need to examine the issues," he said in a video carried by Iranian media.

"But what's important is that we are moving forward so that we gradually get into the details," Araghchi said.

The Trump administration has kept piling on sanctions despite the talks, angering Iran. On Thursday, the United States imposed sanctions on another refinery in China, the main market for Iranian oil.

Since Trump's withdrawal from the Obama-era deal, the United States has used its power to try to stop all other countries from buying Iranian oil.