Iran has more than tripled its ability to produce enriched uranium in the last three months, adding some 1,000 centrifuges which are used to separate radioactive particles from the raw material.
The development means Iran could have enough material for a nuclear bomb by 2009, sources familiar with the dramatic upgrade tell ABC News.
The sources say the unexpected expansion is taking place at Iran's nuclear enrichment plant outside the city of Natanz, in a hardened facility 70 feet underground.
A spokesperson for the United Nation's International Atomic Energy Agency, the IAEA, declined to comment citing the "extreme sensitivity" of the situation with Iran.
Iran has already declared its above-ground operations at Natanz have some 320 centrifuges.
The addition of 1,000 new centrifuges, which are not yet operational, means Iran is expanding its enrichment program at a pace much faster than U.S. intelligence experts had predicted.
"If they continue at this pace, and they get the centrifuges to work and actually enrich uranium on a distinct basis," said David Albright of the Institute for Science and International Security, "then you're looking at them having, potentially having enough highly enriched uranium for a nuclear weapon in 2009."
Previous predictions by U.S. intelligence had cited 2015 as the earliest date Iran could develop a weapon.
Iranian President Mahmoud Ahmadinejad has publicly predicted his country would have 3,000 centrifuges installed by this May, but few in the West gave his claim much credence, until now.
"I think we have all been caught off guard. Ahmadinejad said they would have these 3,000 installed by the end of May, and it appears they may actually do it," Albright said.
The new centrifuges are in open defiance of the U.N. Security Council which last week imposed a new set of sanctions on Iran for refusing to halt enrichment.
Iran maintains its enrichment facilities are only meant to produce fuel for nuclear power reactors.
But the uranium they are enriching could not be used in the Russian nuclear power reactor they are currently building.
State Department spokesman Sean McCormack declined to comment on the details of Iran's new centrifuges but told ABC News, "This kind of expansion of Iran's centrifuge capability is why we went to the U.N. Security Council and pushed for a stronger resolution and stronger sanctions."
