Tehran has agreed to take seven practical, preliminary measures on nuclear co-operation with the International Atomic Energy Agency by 15 May, Iran said in a statement with the UN watchdog on Sunday.
The development - although limited for now - marked a step forward in an international push to settle a decade-old dispute over Iran's nuclear work, which it says is peaceful but the West fears is aimed at developing a weapons capability.
The agreement could also send a positive signal to separate, high-stakes negotiations between Iran and six world powers which are due to start on 18 February 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 the country'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 UN 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" - fast-functioning equipment that could be used for nuclear weapons.
Although such detonators have some non-nuclear uses, they can also help set off a nuclear explosive device.
"It is potentially an important first step" in resuming the IAEA's investigation, one Western diplomat said, adding that much more was needed to fully clarify its concerns.
Suggesting that more sensitive issues would have to wait a while longer, there was no mention in a joint IAEA-Iran statement of the agency's long-sought access to the Parchin military site, where it suspects explosives tests relevant for nuclear bombs may have been conducted a decade ago.