A UN report saying inspectors found traces of  weapons-grade uranium at an Iranian nuclear facility has fuelled concerns about Tehran running a secret nuclear weapons programme.

Iran, however, contends that the traces were from equipment purchased abroad decades ago.

In a report prepared for the International Atomic Energy Agency board meeting, which begins September 8 in Vienna, made available to a wire service, inspectors said they found particles of highly enriched uranium that could be used in a weapons program. Recently, a report said Pakistan had been helping Iran build a secret nuclear facility.

While Washington suspects Iran of secretly developing chemical and nuclear weapons, Tehran has consistently claimed that its nuclear programme is devoted only to generating electricity.

Speaking to a news agency, Iran's envoy to the IAEA, Ali-Akbar Salehi, claimed that the IAEA's findings were from  equipment that was 'contaminated' with enriched uranium before it was purchased by Iran. But since these were bought long ago through agents, it was impossible to trace their source.

Earlier, Salehi had expressed Tehran's willingness to negotiate an IAEA request to allow more intrusive inspections. The talks are likely to begin after the IAEA assembly convenes in mid-September.   

Despite constant American pressure, the Russians are helping Iran build its first nuclear reactor at Bushehr, which is likely to be completed late next year. Talks are on for two more reactors.