Iran has resumed talks on its nuclear programme with the International Atomic Energy Agency (IAEA), the official IRNA news agency said, in discussions expected to broach sensitive military-related issues.
The day-long discussions with the Vienna-based agency will build on a framework deal agreed in November that required Tehran to take six practical steps by next Tuesday.
With completion of those measures - including a visit to an unfinished heavy-water reactor at Arak - negotiations on "more difficult things" are expected to begin, said Yukiya Amano, the IAEA chief.
Behrouz Kamalvandi, the spokesman for the IAEA, said the meeting had been scheduled for one day but might be extended, the IRNA quoted him as saying on Friday.
The "aim is to answer the IAEA's questions", Kamalvandi said, without elaborating.
On its website, Iran's state-run Press TV cited the same official as saying Iran was "ready to answer all IAEA questions".
Kamalvandi has said that, based on the IAEA's assessment of progress, the scope of future co-operation will be decided.
He expressed hope that "the agency's doubts have been removed".
Led by chief inspector Tero Varjoranta, the IAEA team met Iranian nuclear officials, led by Iran's IAEA envoy, Reza Najafi.
The six-step November deal was struck after two years and nearly a dozen rounds of talks.
That deal is separate to the landmark nuclear agreement also reached in November with the five permanent members of the UN Security Council - Britain, China, France, Russia and the United States - as well as Germany. The deal put temporary curbs on Iran's nuclear activities.
Implementation began on December 8 when IAEA inspectors visited Arak, whose small, unfinished heavy-water reactor has been hit by a series of delays.
Diplomats are cautiously optimistic that after Saturday’s talks the team of senior IAEA inspectors will be able to show at least some progress in gaining Iran's cooperation.
Tehran-IAEA relations have improved since last year's election of a relatively moderate, Hassan Rouhani, as president of Iran on a platform to ease the country's international isolation.
Rouhani said this week in a televise address that his country had started to benefit from the deal.
One Vienna-based envoy said there was an expectation that at least one issue related to the IAEA's inquiry into what it calls the "possible military dimensions" to Iran's nuclear programme would be among the next steps to be taken by Tehran.
"It is quite a crucial meeting," the diplomat added.
The IAEA wants Iran to clarify alleged activities in a range of areas of potential application to developing bombs, including various experiments and computer calculations.