U.N. inspectors visited an Iranian plant on Sunday linked to a planned heavy-water reactor that could yield nuclear bomb fuel, taking up an initial offer by Tehran to open its disputed nuclear programme to greater scrutiny.
The increased transparency is the result of a thaw in relations between Iran and the West that culminated in a deal struck last month under which Tehran is to curb its nuclear programme in return for some easing of sanctions.
It was the first time in more than two years that the International Atomic Energy Agency (IAEA) had been allowed to go to the Arak heavy water production plant, which is designed to supply a research reactor under construction nearby.
Iran's heavy water work is a big concern for the West because it could be used in the process of making a nuclear bomb. Tehran says its programme is for peaceful purposes.
Two inspectors arrived in Tehran on Saturday and met experts from Iran's own atomic energy agency before travelling to Arak in the evening, Iran's ISNA news agency reported.