Iranian and foreign nuclear experts gathered in Istanbul on Monday to discuss Tehran's controversial atomic programme, a European Union spokeswoman said.
"The meeting is taking place at the expert-level as planned," said Maja Kocijancic, spokeswoman for EU foreign policy chief Catherine Ashton, who is leading talks between Iran and the so-called P5+1 -- Britain, China, France, Russia, the United States and Germany.
The closed-door meeting is being held in a secret location in the Turkish city, Kocijancic added.
The West and Israel suspect Tehran is seeking to develop nuclear weapons under the guise of what the Islamic republic insists is a purely civilian programme with peaceful ends.
Last week, US President Barack Obama said Iran was "over a year or so" from getting a nuclear bomb, warning that the military option remained on the table.
"We think that it would take over a year or so for Iran to actually develop a nuclear weapon, but obviously, we don't want to cut it too close," he said on Thursday in an interview with Israel's Channel 2 television.
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Should diplomacy fail, all options remained "on the table" for stopping Iran, he said.
Iran and the P5+1 resumed discussions over the decade-old dispute late February after a months-long break and failed meetings in Istanbul, Baghdad and Moscow.
The talks -- held in Kazakhstan -- saw the five UN Security Council members and Germany offer Iran a softening of non-oil or financial sector-related sanctions in exchange for concessions over Tehran's sensitive uranium enrichment operations.
The offer reportedly involves easing sanctions on Iran's gold and precious metals trade and lifting some very small banking operations.
In return, it demands a tougher nuclear inspection regime and the interruption of enrichment operations at the feared Fordo bunker facility where 20-percent enrichment goes on.
The talks were praised by Tehran as a possible turning point in the dispute, and the next political-level meeting takes place in the Kazakh city of Almaty on April 5-6.