The existence of the Fordow plant beneath a mountain near the holy city of Qom was only revealed in September 2009, prompted by its imminent disclosure by Western countries. Iran had already been conducting years of work on the facility, slated to hold roughly 3,000 centrifuges, and at the time it was in an “advanced state of construction,” according to the IAEA, which was first allowed inside the facility in October 2009.
In 2011, Iran told the IAEA that it will use Fordow to continue to enrich uranium to 20 percent, a process which the UN told Tehran to halt. Centrifuge installation there has begun, as has the transfer of low-enriched uranium for further refining. In August 2012, the IAEA reported that the number of centrifuges at Fordow had more than doubled to 2,140, up from 1,064 in May. But the IAEA said the additional centrifuges were not yet operational.