The announcement that this second cascade doubles Iran's uranium enrichment capability came as world powers worked on a draft resolution in the UN Security Council to impose limited sanctions on Teheran because of its refusal to cease enrichment a process that can produce material for nuclear power reactors, or weapons.

The Iranian Students News Agency (ISNA) quoted an anonymous official on Friday as saying that Iran has begun injecting gas into its second network of centrifuges and has obtained successful enrichment results.

"We are injecting gas into the second cascade, which we installed two weeks ago," ISNA quoted the anonymous official as saying.

The news agency said Iran's capacity to enrich uranium had doubled with this second centrifuges cascade.

"We have already exploited the product of the second cascade," said the official, implying that engineers had succeeded in the enrichment process.

In a separate report on Friday, ISNA quoted Ali Larijani, Iran's top nuclear negotiator, as saying that the expanded enrichment programme should not hinder negotiations with the West.

"It is possible to review both nuclear and regional issues through negotiation," Larijani was quoted as saying.

He called for an open negotiation on the enrichment issue, and blamed the West of being irrational in its opposition to an Iranian nuclear programme, which Teheran says is geared toward purely civilian use such as generating electricity.

"Negotiations should be held in a rational and free climate," Larijani said. "We cannot attend conditional talks."