Iran's recently revealed uranium enrichment hall is a highly fortified underground space that appears too small to house a civilian nuclear program, but large enough to serve for military activities, diplomats told The Associated Press on Thursday.
Iran began building the facility near the holy city of Qom seven years ago, and after bouts of fitful construction could finish the project in a year, the diplomats said.
Both the construction timeline and the size of the facility - inspected last month by the International Atomic Energy Agency - are significant in helping shed light on Teheran's true nuclear intentions.
Iran says it wants to enrich only to make atomic fuel for energy production, but the West fears it could retool its program to churn out fissile warhead material.
One of the diplomats - a senior official from a European nation - said Thursday that the enrichment hall is too small to house the tens of thousands of centrifuges needed for peaceful industrial nuclear enrichment, but is the right size to contain the few thousand advanced machines that could generate the amount of weapons-grade uranium needed to make nuclear warheads.
The pauses in construction may reflect Teheran's determination to keep its activities secret as far back as 2002, when Iran's clandestine nuclear program was revealed.
Citing satellite imagery, the diplomats said Iran started building the plant in 2002, paused for two years in 2004 - the same year it suspended enrichment on an international demand - and resumed construction in 2006, when enrichment was also restarted.
Since then, Iran has defied three sets of UN Security Council sanctions aimed at forcing it to again freeze uranium enrichment.
All of the diplomats have access to information compiled by the IAEA, and demanded anonymity in exchange for discussing confidential matters with the AP.
Iran informed the IAEA only in September that it was building the facility near Qom, leading the US, British and French leaders to denounce Teheran for keeping its existence secret. IAEA inspectors visited the plant last month.
Iran says it fulfilled its legal obligations over when it revealed the plant's construction, though IAEA chief Mohamed ElBaradei has said Teheran was "outside the law" and should have informed his agency when the decision to construct was made.
Western officials suspicious of Teheran's nuclear program believe the Islamic Republic only decided to inform the IAEA after it became convinced that the plant's existence had been noted by foreign intelligence services.
The Qom facility is the second known Iranian plant designed for enrichment. The first facility at Natanz, revealed by Iranian dissidents in 2002, has since grown to house around 9,000 centrifuges and has churned enough low-enriched uranium to turn into material for one or two nuclear warheads.
Low-enriched material is suitable for what Iran says will be a nationwide nuclear power grid. But that stockpile can be enriched further to weapons grade warhead material.
After years of expansion, the Natanz program, which relies on antiquated centrifuges based on black market imports, appears to be running into problems associated with increasing the number of operating centrifuges.
The senior diplomat said Iran was only using about 5,000 of the centrifuges set up at Natanz which were turning out about 80 kilograms - less than 200 pounds - of low-enriched uranium a month. That, he said, amounted to roughly the same output using the same number of machines as in September, when the IAEA last reported on Iran to its 35 board member nations.
He said breakdowns and maintenance of the old centrifuges appeared to account for the stagnation. In contrast, the facility near Qom appears designed to shelter fewer but more modern models configured to churn out more enriched material faster.
International hopes that Iran was ready for at least a partial concession on enrichment were raised after Teheran signaled in early October it was ready to send most of its enriched Natanz stockpile abroad to be turned into metal fuel for its small research reactor. Teheran would have needed at least a year to produce enough new material to replace what it shipped out, thereby delaying its ability to produce weapons-grade uranium should it have chosen to do so.
Since then, however, Iranian officials have overwhelmingly - if unofficially - rejected exporting most of their enriched uranium.
The senior diplomat said nuclear negotiators from the US, Russia, China, Britain, France and Germany - the six nations trying to entice Teheran into enrichment concessions - planned to meet next week to discuss further strategy, including the possible threat of new UN sanctions on Teheran for its nuclear defiance.