"Iran is in the process of installing 3,000 centrifuges at Natanz and currently has 1,600 centrifuges working," said Abdolreza Rahmani Fazli, the deputy to top nuclear negotiator Ali Larijani.

The statement confirms reports Wednesday from diplomats at the International Atomic Energy Agency (IAEA) talks in Vienna.

They said Iran had managed to speed up some centrifuges and was beginning to move towards enrichment at an industrial level.

The latest announcement came despite a warning from US President George W. Bush earlier Thursday that Britain and the United States would push for fresh sanctions against Iran if it refused to rein in its nuclear programme.

The United Nations has already adopted two resolutions imposing sanctions on Iran for defying calls to halt its sensitive uranium enrichment work. Tehran denies Washington's charge that it seeks nuclear weapons.

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