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, an Iranian official said Thursday.

Iran and world powers are trying to strike a deal that would prevent Tehran from developing a nuclear bomb, a goal it denies having, in return for an easing of punishing economic sanctions.

Zarif and Kerry will hold two days of discussions from Sunday after their diplomats begin bilateral talks on Friday, Iran's deputy foreign minister Abbas Araqchi said.

"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," Araqchi was quoted as saying by the official IRNA news agency.

He was referring to Britain, China, France, Russia, the United States and Germany, which are seeking to thrash out a complex deal with Iran.

"These bilateral consultations will take place in the context of the P5+1 nuclear negotiations with Iran," the US State Department said, adding that the European Union's deputy foreign policy chief Helga Schmid would also join the talks.

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.

But scepticism is mounting about whether a permanent agreement is possible, after two deadlines for a comprehensive deal were missed.

- 'Complicated' negotiations -

Separately, the International Atomic Energy Agency said in a report Thursday that Iran still had not responded to specific questions on allegations that it had previously carried out nuclear weapons research.

Tehran has consistently rejected the claims, but agreed to respond to questions on the subject. It however has not provided explanations due in August 2014 on two specific points.

Zarif has met multiple times with Kerry, most recently in Munich earlier this month on the sidelines of a global security conference, when both spoke out against any further deadline extensions.

Negotiators are now working toward reaching a political framework for a deal by March 31, with the final technical details to be laid out in a comprehensive accord by June 30.

"The problem is that for now, Iran has not yet demonstrated to us that it intends to renounce the bomb," French President Francois Hollande said Thursday.

"But once that is done, the agreement will be concluded."

Iran's supreme leader Ayatollah Ali Khamenei has voiced opposition to the two-stage accord process.

"Any agreement must come in one step, and include both a general framework and details" of a deal, he said earlier in February.

China's Foreign Minister Wang Yi, speaking in Tehran last week, said the negotiations had seen "positive progress" but had become "more difficult and complicated" as they near conclusion.

Israel, the region's sole if undeclared nuclear-armed state, reiterated on Thursday its opposition to the negotiations between Tehran and the West, and renewed its accusation that Iran is seeking a nuclear bomb.

"The Iranian regime aspires to acquire nuclear capability. This regime has to be stopped," Israeli Defence Minister Moshe Yaalon said during a visit to India.

"Iran is the main instigator of instability in the Middle East," he said.