Diplomats in Vienna negotiating a renewal of the 2015 Iran nuclear deal agreed to fast-track efforts to return Tehran and Washington to compliance.
The third round of talks began amid signs of progress being made in the meetings that Iran is holding with the accord's remaining signatories, China, France, Germany and the UK.
“The discussions proved that participants are guided by the unity of purpose, which is full restoration of the nuclear deal in its original form,” said Mikhail Ulyanov, Russia’s envoy to the talks.
“It was decided to expedite the process.”
Iran's Foreign Ministry said "the participants decided to speed up the process of negotiations", in another sign that the 2015 deal, which Tehran signed with world powers to limit its nuclear capabilities, could be revived.
Former US president Donald Trump unilaterally withdrew from the accord in 2018 and reimposed heavy sanctions on Iran as part of his “maximum pressure” campaign on the country.
In response, Iran repeatedly breached the terms of the deal. It says it will only return to compliance once the administration of Mr Trump’s successor Joe Biden removes the sanctions.
Mr Biden wants a return to the deal and a US delegation is in Vienna, although it is not talking directly to Iran.
Germany’s Foreign Minister Heiko Maas, who is not in Vienna, said the talks were “anything but easy,” but that everyone was working to keep the deal alive.
"We hope all parties will sustain the momentum we have already reached in their efforts towards an earliest resolution of this issue before us," said Wang Qun, China's envoy.
Expert groups are working on proposals to resolve the problems relating to the sanctions and Iranian compliance, as well as the “possible sequencing” of Washington’s return to the deal.
Earlier on Tuesday, Iranian government spokesman Ali Rabiei hinted at possible future prisoner swaps with the US. Last week, a Foreign Ministry official in Tehran also suggested an exchange of prisoners could form part of the discussions in Vienna.