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Iran retaliated by beginning to enrich uranium to 60% purity at its Fordo nuclear plant.

Last year the global nuclear watchdog found uranium particles enriched to 83.7% purity - very close to weapons grade - at Iran's underground Fordo site.

The new Natanz facility is likely to be even deeper underground than Iran’s Fordo facility, another enrichment site that was exposed in 2009 by U.S. and other world leaders.

The intelligence on Fordo that Mr. Akbari provided was one of the revelations that the British intelligence official passed on to Israeli counterparts and other friendly agencies in 2008, according to three Western intelligence and national security officials.

In April 2008, Britain received and shared with Israel and Western agencies the intelligence about Fordo, a uranium enrichment facility deep inside an underground military complex, that was part of Iran’s efforts to build a nuclear bomb.