Iran's progress in developing uranium enrichment is slow and recent additions to its nuclear fuel production complex have only been older-model centrifuges, the head of the UN atomic watchdog chief said.

Mohamed ElBaradei, director of the International Atomic Energy Agency, said Iran had between 3,300 and 3,400 centrifuges of the 1970s vintage P-1 type operational in the Natanz enrichment hall, up from 3,000 at the end of last year. He urged Iran to refrain from speeding up its enrichment campaign until a dispute between the Islamic Republic and world powers over suspicions about its nuclear intentions was resolved.

Iran says it wants to produce nuclear fuel only for electricity so it can export more oil.

However, the United Nations has imposed three sets of sanctions on Tehran for hiding the work from the IAEA until 2003, failing to prove to inspectors since then that it is wholly peaceful and refusing to suspend the programme.

"They are basically making some centrifuges of the old type, the P-1 centrifuges that have already been there. The rate of progress on that has not been very fast," ElBaradei told a news conference during a visit to Berlin.

"I think they had 3,000 centrifuges in the past and now they have 3,300 or 3,400 so they are not moving very fast. "I continue to call on Iran not to speed the process because we first need to have an agreement before Iran moves forward with its enrichment programme."

Iran said last week it had installed almost 500 more centrifuges at Natanz under plans to bring a further 6,000 on line.