"We have 6,000 centrifuges working and we plan to increase them. In the next five years we plan to have 50,000 centrifuges," Atomic Energy Organisation Gholam Reza Aghazdeh told reporters.

He was speaking at a press conference in the Gulf port of Bushehr where Iran began testing its first nuclear power plant, which has been built by Russia.

In November, Aghazdeh said that Iran was operating more than 5,000 uranium enrichment centrifuges at its facility in Natanz.

Last week, the UN's atomic watchdog said in a report that Iran was continuing to enrich uranium, a process potentially used to make an atom bomb, but has slowed down the expansion of its activities.

"Contrary to the decisions of the Security Council, Iran has not suspended its enrichment related activities," the International Atomic Energy Agency wrote in its latest report on Tehran's contested nuclear drive.

Enrichment is at the heart of Western fears that Iran is secretly trying to develop nuclear weapons as it can be used both to make nuclear fuel and the fissile core of an atom bomb.

The report by the IAEA, which has been investigating Iran's nuclear programme for six years, said there were 3,964 centrifuges actively enriching uranium in Natanz, just 164 more than in November.

On top of those, a further 1,476 centrifuges were undergoing vacuum or dry run tests without nuclear material and an additional 125 had been installed but remained stationary.

Iran vehemently denies it has nuclear weapons ambitions and has defied five UN Security Council resolutions calling for a freeze in enrichment activities, including three imposing sanctions.

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