Delegations from Russia and the US involved in nuclear negotiations with Iran held talks in Vienna on Monday, two days before a summit between US President Joe Biden and Russian leader Vladimir Putin.
The US is not directly involved in the Vienna negotiations but has regular contacts with diplomats taking part.
Efforts to revive a 2015 nuclear containment deal for Iran are a rare topic of collaboration between the two adversaries.
Mikhail Ulyanov, a senior diplomat who led the Russian delegation at the meeting in Vienna, called the talks with US envoys “fruitful".
“Our dialogue in Vienna seems to be proof that the two countries can maintain business-like co-operation on issues of common interest, non-proliferation in this particular case,” Mr Ulyanov wrote in a tweet.
The administration of former president Donald Trump pulled the US out of the nuclear accord in 2018, saying it gave Iran too many concessions.
Diplomats from China, Germany, France, Russia, and Britain held joint talks with Iran Saturday and bilateral meetings afterwards at a hotel in the centre of the Austrian capital.
Matthew Rojansky, director of the Wilson Centre’s Kennan Institute in Washington, said Russia was keen to limit some of Iran’s ambitions.
“Moscow still prefers to see Tehran checked in its aspiration to develop a weapon, but is much less motivated when it comes to checking Iran’s regional ambitions and its broader global misbehaviour,” Mr Rojansky told AP.
“At the same time, Russia has a balancing act to perform in Syria, where Iran’s force of arms on the ground could become a problem for Russian ambitions.”
The 2015 agreement was designed to keep Iran’s nuclear programme peaceful, imposing strict controls on uranium enrichment levels and the technology and facilities used for the process.
Iran stopped abiding by those limits after the US withdrawal but insists it has no plan to build nuclear weapons – a claim that the US and its western allies dispute.