The move was expected. Tehran had committed to convert or dilute its 20-per cent enriched stockpile under an agreement with six powers last November that froze its atomic programs pending negotiations on a comprehensive deal. Those talks were extended Saturday to Nov 24.
Still, the development was noteworthy in reflecting Iran's desire not to derail the diplomatic process with the six countries the United States, Russia, China, Britain, France and Germany.
Iran had more than 200 kilograms (over 250 pounds) of 20 per cent enriched uranium when the preliminary agreement was reached. That's nearly enough for one warhead.
At 20 per cent, enriched uranium can be converted quickly to arm a nuclear weapon. Iran denies wanting such arms.
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Tehran is keen to seal a deal that would end nuclear-related sanctions on its economy, but is resisting a US-led drive to put stiff, long-term constraints on atomic activities that have both peaceful and weapons-related applications.
The main dispute is over uranium enrichment, which can make both reactor fuel and the fissile core of nuclear warheads.
It now has about 20,000 centrifuges, with half of them operating. Iranian officials have recently signaled they are ready to freeze that number for now. But US Secretary of State John Kerry said last week it was "crystal clear" that even 10,000 are too many.
Diplomats say Washington wants no more than 2,000 of the machines.