The new round will come a week after the longtime foes held their highest-level negotiations since US President Donald Trump abandoned a landmark nuclear deal in 2018.

"Although we have serious doubts about the intentions and motivations of the American side, in any case we will participate in tomorrow's negotiations," Araghchi said during a press conference in Moscow with his Russian counterpart Sergei Lavrov.

Araghchi will set off on Saturday for Rome for a fresh round of Omani-mediated talks with US Middle East envoy Steve Witkoff.

"We are fully prepared to pursue a peaceful resolution for Iran's peaceful nuclear programme," Araghchi said.

Lavrov said Moscow was ready "to play any role that will be useful from Iran's point of view and that will be acceptable to the United States."

Russia, which commands the world's largest confirmed arsenal of nuclear weapons, has deepened its military ties with Iran since it launched its offensive on Ukraine in February 2022.

Western countries including the United States have long accused Iran of seeking to acquire nuclear weapons -- an allegation Tehran has consistently denied, insisting that its programme is for peaceful civilian purposes.

On Tuesday, Iran's Islamic Revolutionary Guard Corps said the country's military capabilities were off limits in the discussions.

The official IRNA news agency reported Iran's regional influence and its missile capabilities -- long criticised by Western governments -- were among its "red lines" in the talks.

On Wednesday, the Iranian foreign minister said Iran's enrichment of uranium was not up for discussion, after Witkoff called for it to end.

"If there is similar willingness on the other side, and they refrain from making unreasonable and unrealistic demands, I believe reaching an agreement is likely," Araghchi said during the press conference.

Lavrov emphasised that any potential agreement should only pertain to the nuclear issue.

"This is a fundamental point that must be taken into account by those who try to burden the negotiations with non-nuclear issues and thus create a very risky situation," he said.