The report said that Tehran had more than tripled its ability to produce enriched uranium in the past three months, adding some 1,000 centrifuges which are used to separate radioactive particles from the raw material.
The development meant Iran could have enough material for a nuclear bomb by 2009, it quoted sources familiar with the dramatic upgrade as saying.
The unexpected expansion is taking place at Iran’s uranium enrichment facility in Natanz, the report said.
Iran had previously informed the United Nations nuclear watchdog that it had 320 centrifuges running in Natanz.
A spokesperson for the International Atomic Energy Agency said that there was an “extreme sensitivity” in the situation with Iran.
Previous predictions by U.S. intelligence had cited 2015 as the earliest date for Iran to be able to develop a nuclear weapon.
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, the report added.
