"The rate of progress so far has not been very fast" at Iran's Natanz plant, ElBaradei said after talks with German Foreign Minister Frank-Walter Steinmeier in Berlin.

"I think they had in the past 3,000 centrifuges and I think now they have like 3,300 or 3,400. They are not moving very much."

Iranian President Mahmoud Ahmadinejad said on April 8 that the country had started work on installing 6,000 new centrifuges at Natanz and last week Iran's official IRNA news agency said it was now operating 492 new ones.

The United States warned last week that Tehran risked further isolation and new international sanctions for its continued refusal to comply with UN resolutions.

"I continue to call on Iran not to speed up the process because we need first to have an agreement with the international community about building confidence before Iran moves with its enrichment programme," ElBaradei said in Berlin.

Western governments believe Tehran is trying to develop nuclear weapons, but Tehran insists its programme is peaceful and aimed at generating energy. Enriched uranium can be used for both purposes.

ElBaradei was speaking on the sidelines of a two-day international conference on nuclear power in Berlin which began on Thursday.

The five veto-wielding members of the UN Security Council, plus Germany and the EU, failed on Wednesday to agree on an agenda for negotiations with Iran over its nuclear programme, an official said.

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

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