TEHRAN, (Reuters) – Iran said on Friday it had installed almost 500 more centrifuges at its Natanz uranium enrichment complex, the official IRNA news agency reported, defying international demands that it halt such work.

The West fears Iran is trying to covertly produce nuclear bombs under cover of a civilian programme, and the U.N. security Council has imposed three sets of sanctions on Iran for refusing to halt uranium enrichment work. “Three new cascades of 164 centrifuges have been installed in Natanz facility and are working,” an unnamed official told IRNA. “These centrifuges are P1 type.”

Iran launched 3,000 centrifuges, a basis for industrial scale enrichment, in the Natanz facility last year. But they are the 1970s-vintage P1 design, prone to breakdown.

It says it has now begun installing 6,000 new centrifuges at Natanz, in central Iran, and that it has begun testing an advanced centrifuge in Natanz’s pilot wing — speeding up work that could give it the means to make atom bombs if it chooses.

Iran, the world’s fourth largest oil exporter, says it wants nuclear technology only to generate electricity. Enriched uranium can be used as fuel in power plants or, if refined much further, provide material for nuclear weapons.

Mohammad Saeedi, the deputy head of Iran’s Atomic Energy Organisation, on Friday denied reports that Iran was having difficulties in running its centrifuges at full capacity. “There are no technical problems regarding the development of centrifuges,” he told IRNA.

Iran says it plans eventually to have 50,000 centrifuges to help produce fuel for a planned network of power plants.