The U.N. nuclear agency said on Sunday that Iran had agreed to start addressing suspicions that it may have worked on designing an atomic weapon, a potential breakthrough in a long-stalled investigation into Tehran's atomic activities.
The development - although limited for now - marked a step forward in an international push to settle a decade-old dispute over Iran's nuclear programme. Tehran says this is peaceful, while the West fears that Iran wants to develop atomic arms.
The deal could also send a positive signal to separate, high-stakes negotiations between Iran and six world powers which are due to start on Feb. 18 in Vienna, aimed at reaching a broader diplomatic settlement with the Islamic state.
Efforts to end years of hostile rhetoric and confrontation that could otherwise trigger a new war in the Middle East gained momentum with last year's election of a relative moderate, Hassan Rouhani, as new Iranian president on a platform to ease Iran's international isolation.
The International Atomic Energy Agency said Iran had agreed during talks in Tehran to take seven new practical measures within three months under a November transparency deal with the IAEA meant to help allay concern about the nuclear programme.
For the first time, one of them specifically dealt with an issue that is part of the U.N. nuclear agency's inquiry into what it calls the possible military dimensions to Iran's atomic activities. Iran has repeatedly denied any such ambitions.
It said Iran would provide "information and explanations for the agency to assess Iran's stated need or application for the development of Exploding Bridge Wire detonators".
Although such fast-functioning detonators have some non-nuclear uses, they can also help set off an atomic device.
"It is an important issue and it is good that the agency can now tackle it," former chief IAEA inspector Herman Nackaerts said. But he made clear that much work remained in order to fully clarify the IAEA's concerns: "It is a first step in a long process."
Faced with deadlock last year in its attempts to get Iran to cooperate with its investigation, the IAEA changed tactics and now seeks to gradually build mutual trust by starting with some of the less sensitive issues, diplomats say.
Suggesting that more difficult matters would have to wait a while longer, there was no mention in the IAEA's statement of its long-sought access to the Parchin military site, where it suspects explosives tests relevant for nuclear bombs may have been