An international team of scientists has found no evidence of Iranian efforts to produce nuclear arms.
The team said traces of enriched uranium earlier discovered in that country came from centrifuges it bought from Pakistan's scientist A Q Khan.
The traces of enriched uranium found in Iran had led to suspicions of a nuclear weapons programme and strong United States demands for action against Tehran. The scientists have now confirmed that those traces came from centrifuges Iran bought from Khan.
"The biggest smoking gun that everyone was waving is now eliminated with these conclusions," a senior US official told 'The Washington Post'.
Scientists from the US, France, Japan, Britain and Russia met in secret during the past 9 months to pore over data collected by inspectors from the International Atomic Energy Agency, according to US and foreign officials.
Iran has long contended that the uranium traces were the result of contaminated equipment bought 9 years ago from Khan.
But the Bush Administration had pointed to the material as evidence that Iran was making bomb-grade ingredients.
John R Bolton, US ambassador to the United Nations who had earlier served as the Bush administration's pointman on nuclear issues, had suggested during Congressional testimony in June 2004 that the Iranians were lying about the contamination.
The Iranians have now been proved right and Bolton and other administration leaders who echoed him have been proved wrong.
The conclusion of the international team will now be shared with IAEA board members in a report due to be out in the first week of September, according to US and European officials, who agreed to discuss details of the investigation with 'The Post' only on condition of anonymity.
The report 'will say the contaminants issue is resolved,' a western diplomat told the paper.
Iran built its nuclear programme in secret over 18 years with the help of Khan, who sold spare parts from Pakistan's own weapons programme to Iran, Libya and North Korea.