Senior UN officials are holding a third round of talks in Tehran to discuss Iran's nuclear programme.
The UN delegation is led by Olli Heinonen, an IAEA deputy director
In July, the two sides announced a two-month arrangement aimed at clearing up outstanding questions and giving the IAEA better access to nuclear sites.
Under threat of further UN sanctions, Iran appears anxious to co-operate and has kept to the timetable it agreed with the UN, a BBC correspondent says.
Iran insists that its nuclear programme is entirely peaceful.
But the UN Security Council has already passed two rounds of sanctions against Iran designed to make it harder for Iran to pursue its nuclear programme, and Washington alleges that Iran is secretly attempting to build a nuclear weapon.
A deputy director general of the International Atomic Energy Agency (IAEA), Olli Heinonen, will hold two days of discussions with Javad Vaeedi, a deputy to Iran's chief nuclear negotiator, Ali Larijani.
Since July's agreement, Iran has allowed the IAEA's inspectors to visit its heavy water research reactor at Arak, and has been holding talks with a UN technical team on guidelines for inspecting its uranium enrichment plant at Natanz.
BBC Iran analyst Pam O'Toole says that over the past few months, Iran has appeared anxious to demonstrate the transparency of its programme.
One Iranian official recently expressed hope that the West could respond to Iran's co-operation with the IAEA by not pushing for more sanctions.
However, some Western analysts have alleged that Tehran is simply trying to play for time, hoping to delay the imposition of further sanctions while it increases its nuclear know-how, our correspondent says.
They also point out that Tehran has continued to refuse to heed the UN Security Council's key demand - that it suspend its uranium enrichment-related activities.