VIENNA: Iran has escalated its uranium enrichment further by enriching with advanced machines at its underground Fordow plant that are able to switch more easily between enrichment levels, the U.N. atomic watchdog said in a report on Saturday seen by Reuters.

The International Atomic Energy Agency verified on Saturday that Iran had begun feeding uranium hexafluoride gas enriched to up to 5% into the cascade, or cluster, of 166 IR-6 centrifuges with so-called modified sub-headers at Fordow, the confidential IAEA report to member states said.

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Iran has informed the IAEA it plans to use the machines to enrich to up to 20% purity, the report said, less than the up to 60% it is producing elsewhere and the roughly 90% of weapons grade. But Western diplomats have repeatedly expressed concern about the modified sub-headers because they make it possible to switch to higher purity levels much more easily and quickly.