Russia wants to see a United Nations arms embargo against Iran lifted "as soon as possible" but it is up to Tehran to accept the terms of a final nuclear deal, Foreign Minister Sergei Lavrov said on Thursday.

He spoke ahead of talks between Russian President Vladimir Putin and Iranian President Hassan Rouhani on the sidelines of a BRICS summit in the Urals city of Ufa.

"We are in favour of lifting the embargo as soon as possible and will support a decision made by Iran's negotiators," Lavrov told reporters.

Russia's top diplomat stressed that the UN Security Council arms embargo had been imposed to force Iran to negotiate, a goal that had "long been reached."

Resumption of arms deliveries would help Iran combat terrorism and Islamic State radicals, he added.

Iranian-backed militias are playing a key role in the fight against the jihadist group in neighbouring Iraq.

"Iran is committed to fighting IS... and lifting the arms embargo will help it improve its ability to fight against terrorism," Lavrov said.

Iran has insisted there should be changes to the UN arms embargo and an easing of restrictions on missile sales, a prospect that alarms rivals of Iran and US allies in the region.

Lavrov left the talks on Iran's nuclear programme in Vienna on Tuesday to attend the summit but said he would fly back to sign the final agreement "at any moment."

"As soon as my participation in Ufa is over I will be ready to join. I hope it will really be a final meeting."

He claimed there were no "insurmountable problems" left to tackle unless somebody tried to deliberately stall the negotiating process.

"We are in the final stages...we have now come right up to the final, all-encompassing agreement. It is within reach," he said.

"Almost daily there are positive steps of progress," Lavrov said of the talks in Vienna. "I expect that nobody will undermine the work that has already been done."

Lavrov spoke as his Western counterparts sought to finalise the deal in Vienna on the eve of a deadline to present it to US lawmakers.

But Russia's top diplomat cautioned against "artificial deadlines".

"As far as deadlines are concerned, we never had artificial deadlines," he said.

"We all agreed that the main thing is the quality of the agreement that should ensure the balance of interests" by securing non-proliferation as well as respecting Iran's rights.