Envoys from Britain, China, France, Russia, the United States, Germany and the European Union started their meeting after Tehran announced last week it had started operating hundreds of new centrifuges at its uranium enrichment plant.
"We are here today to discuss the new developments surrounding the Iranian nuclear issue," China's assistant foreign minister He Yafei said at the start of the one-day gathering.
"We have agreed to discuss new proposals on the Iranian nuclear issue."
The deputy-ministerial-level talks are aimed at seeking a "negotiated solution" to the impasse as agreed by the foreign ministers of the six nations in 2006, he added.
The talks are part of a routine round of meetings set up in 2006 that are hosted by the various countries involved.
Western governments have warned Tehran that it faces further sanctions if it continues to expand its nuclear programme, which they fear is a cover for a drive to develop an atomic weapon.
Tehran insists its programme is entirely peaceful and aimed at generating energy.
But its official IRNA news agency said last week it was now operating 492 new centrifuges at the Natanz uranium enrichment plant, in defiance of UN calls to freeze the process.
The United States said last week that Tehran risked further isolation and new international sanctions for its continued refusal to comply with UN resolutions.
"The Iranian government continues to be in violation of multiple United Nations Security Council resolutions and with each step it takes it continues to isolate its people and risk further international financial and diplomatic sanctions," White House spokesman Gordon Johndroe said.
French Foreign Minister Bernard Kouchner issued a similar warning, saying the international community must consider "reinforced" sanctions if Iran does not respond to concerns about its nuclear work.
