A new report by the International Atomic Energy Agency (IAEA) is expected to show that Iran has installed more uranium enrichment centrifuges at its Fordow Fuel Enrichment Plant - but that they are not yet being used to refine uranium.
Here is a look at the Fordow plant:
* Iran began building the plant in secret as early as 2006. It was publicly revealed by U.S. President Barack Obama, French President Nicolas Sarkozy and British Prime Minister Gordon Brown in September 2009, shortly after their three countries gave the IAEA evidence of the facility.
* IAEA inspectors first visited the site, 20 km (12 miles) north of the holy city of Qom, in October 2009 to verify design data provided by Iran.
- They confirmed it was designed to run with around 3,000 centrifuges, Iran saying the machines might be a more advanced type than it had used before. These could enrich uranium two to three times faster than Iran had done so far, experts said.
- The Institute for Science and International Security (ISIS) has assessed that a fully equipped facility this size would give Iran the capability to secretly make enough weapon grade uranium for one bomb in less than a year. If Iran used 3.5 percent enriched uranium as feedstock, it could make enough weapon grade uranium for a bomb in even less time.
* The plant was built to house a total of 16 cascades, each of 174 enrichment centrifuges, ie a total of roughly 2,800 machines. So far, four cascades are operating (in two pairs) to produce 20 percent enriched uranium.
- Between December 14, 2011, when the first set started production and February 17, 2012, these sets of cascades produced about 13.8 kg of the 20 percent material.
- ISIS said in a report in February that Iran was being ambiguous over the number of centrifuges at Fordow that would make 20 percent uranium. ISIS said Iran was signaling that it intended to fully outfit the plant with centrifuges, despite having no credible civilian need for the refined uranium that these machines would produce.
* In November 2009, the IAEA's 35-nation governing board censured Iran for developing the plant in secret and demanded Iran freeze the project. Iran rejected the demand.
- Earlier this month, Iran again said it would never suspend its uranium enrichment program and saw no reason to close the Fordow underground site, making clear Tehran's red lines in nuclear talks with world powers.
For an Interactive look at Iran's Nuclear Program
please click on link.reuters.com/gad76r
(Reporting by David Cutler, London Editorial Reference Unit)