Iran has still not addressed specific issues that could feed suspicions it may have researched an atomic bomb, a UN watchdog report showed, potentially complicating efforts by six powers to clinch a nuclear deal with Tehran.
The confidential report by the International Atomic Energy Agency (IAEA), obtained by Reuters news agency, said Tehran was continuing to withhold full cooperation in two areas of an IAEA investigation that it was supposed to have given by August last year.
"Iran has not provided any explanations that enable the agency to clarify the outstanding practical measures," the IAEA said, referring to allegations of explosives tests and other activity that could be used to develop nuclear bombs.
Iranian Foreign Minister Mohammad Javad Zarif and top US diplomat John Kerry will meet in Geneva this weekend for talks on Tehran's nuclear programme, Iran's deputy foreign minister Abbas Araghchi said on Thursday.
"After four days of bilateral discussions between the Iranian and US nuclear delegations, they could continue with the participation of all members of the P5+1," Araghchi was quoted as saying by the official IRNA news agency.
Iran and world powers are trying to strike a deal that would prevent Tehran from developing a nuclear bomb, in return for an easing of punishing economic sanctions.
Tehran denies ever seeking atomic weapons but Western powers are unconvinced its activities have been solely aimed at peaceful energy production.
Under an interim deal struck in November 2013, Iran's stock of fissile material has been diluted from 20 percent enriched uranium to five percent in exchange for limited sanctions relief.