Iran and the United States on Sunday in Muscat, Oman, held a fourth round of talks on the future of Iran’s nuclear program, hoping to make progress on a key goal for both President Trump and Iran’s leadership.

Abbas Araghchi, Iran’s foreign minister, said after participating in the negotiations on Sunday that this round had been “more serious and explicit” than previous talks, and that the two sides’ positions had “become closer,” Iranian state media reported.

He said the talks would next pick up within about a week.

Both Iran and the United States have said they want to resolve their decades-old dispute over Iran’s nuclear activities through diplomacy, with Tehran exchanging limits on its nuclear program for the lifting of some U.S. sanctions. But the two sides remain far apart on several critical issues.

The talks are being held by Mr. Araghchi and Mr. Trump’s Middle East envoy, Steve Witkoff, through Omani mediators. Mr. Witkoff has spoken uncompromisingly about Washington’s position in recent days, saying that the Trump administration aims to completely dismantle Iran’s nuclear facilities.

But, in remarks published by Iranian state media on Sunday, Mr. Araghchi said that Iran would not accept such conditions. While it was “possible” for Iran to commit to restricting uranium enrichment “for a short time to build trust,” he said, banning enrichment completely was “not negotiable at all.”

He also criticized the American side for making what he called “contradictory statements,” without specifying what he meant.