Iran is still at least two to three years away from building a nuclear weapon, a British leading think tank reported on Wednesday.

"If and when Iran does have 3,000 centrifuges operating smoothly, the IISS estimates it would take an additional 9 - 11 months to produce 25 kg of highly enriched uranium, enough for one implosion-type weapon," said John Chipman, director of London-based International Institute for Strategic Studies (IISS).

"That day is still 2 - 3 years away at the earliest," Chipman said at the launch of the IISS annual publication "The Military Balance."

Iran was on track to complete its goal of producing 3,000 centrifuges by the end of March or shortly thereafter, said Chipman, adding that at least 500 of these had been obtained from the black market.

"Getting the centrifuge cascades to function properly is then another task of an entirely different order of magnitude, which would take at least another year but probably longer," said he.

The United Nations Security Council passed Resolution 1737 on Dec. 23, 2006, calling on Tehran to suspend its enrichment activities and imposing sanctions on Iran's nuclear and missile programs but was rejected by Iran which vowed to install at least 3,000 centrifuges by the end of March.

(Xinhua News Agency February 1, 2007)