"With reference to the environmental samples taken from some equipment at a technical university in January 2006 ... analysis of those samples showed a small number of particles of natural and high enriched uranium," said the report, which is to be presented at a meeting of the watchdog, the International Atomic Energy Agency (IAEA), in Vienna next week.

Uranium can be enriched to produce nuclear reactor fuel. But if it is enriched to a much greater degree it can be used to manufacture atom bombs. It is enriched by centrifuges arranged in cascades.

A senior UN official said Thursday the new traces of highly enriched uranium that had been found were not of a high enough quality to make weapons.

They had been found on "vacuum equipment" which could be used in centrifuges that can enrich uranium but also have many other functions, the official added.

The equipment was believed to have been taken to the university in Tehran from a physics laboratory at the Lavizan military site in the city before the site was razed in 2004. The Iranian authorities destroyed Lavizan after the IAEA asked to investigate it.

IAEA inspectors took samples from the equipment in January.

The report said Iran had told the IAEA the "equipment had not been acquired for or used in the field of nuclear activities. Iran indicated that it was however investigating how such particles might have been found in the equipment."

IAEA inspectors have in the past found particles of high and low enriched uranium on centrifuge equipment at several sites in Iran.

In those instances, Tehran said the contamination had come from equipment it purchased through black markets abroad and was not a product of its own nuclear work.

The IAEA has been investigating Iran since 2003 and says it is not yet able to certify that the Iranian nuclear program is strictly peaceful.

Iran says its nuclear program is a peaceful drive to generate electricity but the United States claims it is a cover for the secret development of atomic weapons.

Iran has since April 11 been enriching uranium at a centrifuge cascade in Natanz but only to a low level -- up to five percent.

Uranium must be enriched by over 90 percent before it becomes weapons-grade material.

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