Iran agreed Sunday to clarify to the UN atomic agency its need for detonators used in a nuclear device, as part of a probe into allegations of its past weapons work.
The move is part of seven new steps agreed between Iran and the International Atomic Energy Agency to increase transparency over Tehran's controversial nuclear drive.
And it appears to be the first time in years Iran has agreed to tackle IAEA suspicions that its nuclear work prior to 2003 had "possible military dimensions".
The development comes as Iran is set to resume nuclear talks with world powers later this month, after clinching an initial accord in November to curb uranium enrichment and open up nuclear facilities to allay concerns Tehran is seeking to acquire atomic weapons
Capping two-days of talks in Tehran with Iranian officials, the IAEA said Iran agreed to provide "information and explanations for the agency to assess Iran's stated need or application for the development of Exploding Bridge Wire (EBW) detonators."
According to the IAEA, Iran told the agency in 2008 that it had developed EBWs for "civilian and conventional military applications" but has yet to explain its "need or application for such detonators."
Such fast, high-precision detonators could be used in some civilian applications but are mostly known for triggering a nuclear chain reaction, which the IAEA believes form "an integral part of a programme to develop an implosion type nuclear device."
There was no immediate reaction from the Iranian side.
But earlier Iran's envoy to the Vienna-based IAEA, Reza Najafi, said that "seven more practical steps" had been agreed between the two sides in a deal that would be implemented by 15 May.
Six other steps had been agreed under a framework deal struck on 11 November.
In the latest agreement, the IAEA will also have "managed access" to the Saghand uranium extraction mine in and the Ardakan yellowcake facility where an impure state of uranium oxide is prepared to be fed into centrifuges for enrichment.
Officially unveiled in April 2013, the plant in Ardakan receives raw material from Saghand, some 120 kilometres (75 miles) away. It can reportedly produce up to 60 tonnes of yellowcake annually.