Trump, who will visit three other Gulf Arab monarchies, 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.

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.

Steve Witkoff, Trump's friend who has served as his globe-trotting negotiator, will take part in the talks, the fourth since Trump returned to the White House, according to a source familiar with arrangements.

"As in the past, we expect both direct and indirect discussions," the person said on condition of anonymity.

The two sides had voiced optimism after the previous talks, which they said took place in a friendly atmosphere, but they are not believed to have gone into technical detail, and basic questions remain.

US Secretary of State Marco Rubio has insisted that Iran give up all uranium enrichment, even for civilian purposes. Witkoff initially voiced more flexibility before backtracking.

The Trump administration has also kept piling on sanctions despite the talks, angering Iran.

Trump in his first term withdrew from a nuclear agreement with Tehran negotiated by president Barack Obama.

Trump imposed sweeping sanctions on Iran including trying to stop all other countries from buying Iranian oil.