But the envoys agreed to continue to work on a joint proposal aimed at bringing Tehran back to the negotiation table and in line with UN resolutions.

"We discussed how to conduct dialogue and negotiations with Iran... we have agreed on most points in the proposal, however there are some outstanding issues that remain to be resolved," China's assistant foreign minister He Yafei said.

"As soon as an agreement is reached on this proposal..., it will be referred to the Iranian side and at that time we hope the Iranian side will respond positively to it and make its own contributions to a proper settlement."

Britain, China, France, Russia, the United States and Germany and the European Union took part in the talks.

He did not give a timeline for when they hoped to resume negotiations with Tehran, but he said the agenda for the talks should lay out "a comprehensive, durable and proper solution" that covers nuclear energy, political security and economic areas.

Wednesday's one-day deputy-ministerial-level meeting was held after Tehran announced last week it had begun operating hundreds of new centrifuges at its uranium enrichment plant, in violation of a raft of UN resolutions.

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.

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