VIENNA: The UN atomic watchdog said Friday that it has detected traces of higher-grade uranium at a site in Iran, but that Tehran had said it may be down to a technical error.

The International Atomic Energy Agency’s latest quarterly report, seen by AFP, said its analysis showed that the traces were of uranium enriched to purities of 27 per cent at the Fordo site near the holy city of Qom.

Iran has told the IAEA that the site was enriching only to 20 per cent, which was already of concern to the watchdog since the capability to do so shortens the theoretical time needed to enrich to weapons-grade uranium of 90 per cent.

“Iran indicated that the production of such particles ‘above the target value’ may happen for technical reasons beyond the operator’s control,” the report said.

“The agency is assessing Iran’s explanation and has requested further details. On 5 May 2012, the agency took further environmental samples from the same location.... These samples are currently being analysed,” it added.

The report also said that new satellite imagery indicated “extensive activities” were taking place at buildings at the Parchin military site near Tehran which the IAEA says it would like to inspect but Tehran has denied it.

The IAEA said that “virtually no activity had been observed for a number of years” and that the apparent new work “could hamper the agency’s ability to undertake effective verification.”