The United States and Iran will hold a fourth round of nuclear talks Sunday in Oman, officials said, just ahead of a visit to the region by President Donald Trump. 

Trump, who will visit three other Gulf Arab monarchies next week, has voiced hope for reaching a deal with Tehran to curb its nuclear program that would avert an Israeli military strike on Iran's uranium enrichment facilities that could ignite a wider war. He has refused, however, to rule out military action in the event the talks come to naught. 

Iran's top diplomat Abbas Araghchi said that Oman, the mediator in the talks, had proposed Sunday as the date and both sides accepted it.

"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 was quoted as saying by regime media. "But what's important is that we are moving forward so that we gradually get into the details." 

Steve Witkoff, Trump's personal friend serving as his globe-trotting negotiator, will take part in the talks.

American and Iranian representatives voiced optimism after the previous talks that took place in Oman and Rome, saying there was a friendly atmosphere despite the two countries' decades of enmity.

However the two sides are not believed to have thrashed out the all-important technical details, and basic questions remain.