By Leila Gharagozlou, Rosa Rahimi and Betsy Klein, CNN

(CNN) — The latest round of high-stakes nuclear talks between Iran and the US have ended, with Tehran calling them difficult but with both sides agreeing to further negotiations.

Iranian Foreign Ministry spokesman Esmaeil Baqaei confirmed on X that the talks had concluded, saying they were “difficult but useful to better understand each other’s positions and to find reasonable & realistic ways to address the differences.”

A senior Trump administration gave a more positive assessment, telling CNN the discussions “were again both direct and indirect” and lasted over three hours, calling them encouraging.

“Agreement was reached to move forward with the talks to continue working through technical elements,” the official said, adding that the US side was “encouraged by today’s outcome” and looks forward to their next meeting “which will happen in the near future.”

No date has been agreed for the next round although Baqaei said it would be announced by mediator Oman.

Omani Foreign Minister Badr Albusaidi said the fifth round of talks would take place once both sides have consulted their leaders. He said Sunday’s discussions included “useful and original ideas” that reflected a shared wish to reach an “honorable” agreement.

Red lines drawn

The talks on Sunday were aimed at addressing Tehran’s nuclear program and lifting sanctions.

That they are happening at all is something of a breakthrough – the talks are the highest-level in years – but signs of firm progress are slim.

Both countries have expressed a willingness to resolve their disputes through diplomacy. A central issue remains Iran’s demand to continue enriching uranium for its nuclear program, which is insists is peaceful, something the US calls a “red line.”

US President Donald Trump, who is headed to the Middle East next week, has threatened that the US would resort to military strikes against Iranian nuclear sites, with Israel’s help, should Tehran fail to reach a deal with its interlocutors.

The Iranian delegation was led by Foreign Minister Abbas Araghchi, who said before the talks got underway that the US side “holds contradictory positions which is one of the issues in our negotiations.”

“We have been clear about our boundaries,” Araghchi added, according to the Fars news agency.

Iranian officials told CNN on Saturday that recent talks with the US were “not genuine” from the American side. The Iranian source also reiterated that allowing uranium enrichment on Iranian soil is Iran’s “definite red line” in the negotiations.

US special envoy Steve Witkoff, who has been heading the American side, warned that if this session of talks were not productive, “then they won’t continue and we’ll have to take a different route.”

Speaking to Breitbart, Witkoff outlined the US’ expectations for the talks, including on the country’s uranium enrichment program. “An enrichment program can never exist in the state of Iran ever again. That’s our red line. No enrichment,” he said.

Iran has said it will not surrender its capability to enrich uranium. The country has long insisted it does not want a nuclear weapon and that its program is for energy purposes.

The head of the International Atomic Energy Agency, Rafael Grossi, warned last month that Iran was “not far” from possessing a nuclear bomb.

“It’s like a puzzle. They have the pieces, and one day they could eventually put them together,” Grossi told French newspaper Le Monde.