The UN atomic watchdog on Sunday started a second day of talks in Tehran on safeguards to enhance transparency on Iran's nuclear drive and allegations of its past weapons work.
The talks are expected to continue into the afternoon, after a first day of meetings was described as "constructive" by Iran's atomic organisation spokesman, Behrouz Kamalvandi.
Iranian media have reported little details of the negotiations with the Vienna-based International Atomic Energy Agency (IAEA) that are expected to broach allegations that Iran's nuclear work prior to 2003, or possibly since, had "possible military dimensions."
There has been no immediate comment from the IAEA team, comprised of chief inspector Tero Varjoranta and four experts who arrived in Tehran late Friday.
The team held talks Saturday with Iranian nuclear officials, led by Tehran's IAEA envoy Reza Najafi, and assessed the implementation of a roadmap deal agreed on November 11.
The deal required Tehran to take practical steps that included visits to the unfinished site of a so-called heavy water research reactor in Arak and a uranium mine in the south.
Also required were information on future research reactors by Iran, identifying sites of new nuclear power plants, and clarification on Iranian statements regarding additional enrichment facilities and laser enrichment technology.
Western powers and Israel suspect that Iran's nuclear drive masks military objectives, a claim Tehran repeatedly denies.