Negotiators for Iran and world powers on Wednesday started their second day of a round of talks in Vienna aimed at hammering out a definitive deal over Tehran's contested nuclear programme by a July 20 deadline.
Although little information has filtered out about the substance of the negotiations, an Iranian representative, Deputy Foreign Minister Abbas Araqchi, said late Tuesday that differences on several issues had been narrowed.
A source close to the talks said the Iranian side sat down with an EU team, ahead of an all-in session later Wednesday with the P5+1 group comprising the United States, France, Britain, Germany, Russia and China.
Iranian Foreign Minister Mohammad Javad Zarif and the European Union's top diplomat, Catherine Ashton, were expected to make a statement to the media afterwards.
The Vienna negotiations are the third round since a November agreement which froze parts of Iran's nuclear programme in return for minimal relief from international sanctions.
That preliminary accord, which came into effect in January, is to expire on July 20, by which time both sides hope to have in place a permanent agreement.
Iran wants to have the crippling sanctions rolled back, while the P5+1 wants Iran's nuclear activities curbed to a point where any breakout point towards atomic weapons would be delayed and easily identified.
Tehran denies it has any ambitions to develop nuclear arms, but has failed to allow verifications that would satisfy the West in particular.
Both sides hope to start work on a draft agreement in their next round, in May.