The European Union has submitted a "final text" at talks to salvage a 2015 deal aimed at reining in Tehran's nuclear ambitions, a European official said on Monday.

"We worked for four days and today the text is on the table," the official, speaking on condition of anonymity, told reporters.

"The negotiation is finished, it's the final text... and it will not be renegotiated."

Major power talks involving Britain, China, France, Germany, Iran and Russia, as well as the United States indirectly, and aimed at reviving an agreement over Tehran's nuclear programme resumed on Thursday in Vienna, months after they had stalled.

"Now the ball is in the court of the capitals and we will see what happens," the European official added. "No one is staying in Vienna."

The official said he hoped to see the "quality" text accepted "within weeks".

Iran said it was examining the text.

"As soon as we received these ideas, we conveyed our initial response and considerations... but naturally, these items require a comprehensive review, and we will convey our additional views and considerations", state news agency IRNA quoted an unnamed foreign ministry official as saying.

On Sunday, Iran demanded the UN nuclear watchdog "completely" resolve questions over nuclear material at undeclared sites.

Iranian sources have suggested a key sticking point has been a probe by the International Atomic Energy Agency (IAEA) on traces of nuclear material found at undeclared Iranian sites.

"That has nothing to do with" the Joint Comprehensive Plan of Action (JCPA) agreement, the European official said.

The UN agency's board of governors adopted a resolution in June, censuring Iran for failing to adequately explain the previous discovery of traces of enriched uranium at three previously undeclared sites.

"We believe that the agency should completely resolve the remaining safeguard issues from a technical route by distancing itself from irrelevant and unconstructive political issues," Iran's foreign minister Hossein Amir-Abdollahian said on Sunday.

The EU-coordinated negotiations to revive the JCPA deal began in April 2021 before coming to a standstill in March.

The 2015 accord gave Iran sanctions relief in exchange for curbs on its nuclear programme to guarantee Tehran could not develop a nuclear weapon -- something it has always denied wanting to do.

But the US unilateral withdrawal from the deal under president Donald Trump in 2018 and the reimposition of biting economic sanctions prompted Iran to begin rolling back on its own commitments.