The traces have been at the heart of an ongoing international dispute over whether Tehran has reneged on its obligations to inform the International Atomic Energy Agency (IAEA) of all enrichment activities.

"IAEA inspectors have reached a tentative conclusion that the contamination came from equipment provided by the nuclear smuggling network headed by Pakistani scientist A.Q. Khan," the specialist magazine said, quoting "sources close to the agency".

It said inspectors believe they can confirm that a sample of uranium enriched to 54 percent, found at one Iranian site, had come from Pakistani equipment.

"The confirmation was only possible after Islamabad gave the IAEA data to verify the uranium source and the US provided a simulation of the Pakistani nuclear programme that matched the account," Jane's said.

A separate contamination sample, of uranium enriched to 36 percent, derived from Russian equipment that Moscow had supplied to China, which in turn passed it on to Pakistan as part of a previous nuclear assistance program, it said.

From Pakistan, it was sold by Khan to Iran, it added.

"The sources note that the origins of several other contamination samples are difficult to trace and may never be known," Jane's said.

It has been known that inspectors from the Vienna-based IAEA had found traces of highly-enriched uranium inside Iran -- leading to suspicions Iran has been trying to produce nuclear bombs and not just atomic energy as it insists.

But Tehran maintained that the traces found their way into the country on equipment bought on an international black market operated by Pakistan's disgraced former nuclear chief, Abdul Qadeer Khan.

Pakistan's foreign minister Khurshid Mahmud Kasuri, on a visit to Tehran, said Monday that Islamabad was cooperating with a UN probe into Iran's suspect nuclear programme.

But he ruled out allowing inspectors into Pakistan as part of the crucial investigation.

In Washington, US President George W. Bush said Monday that Iran "must abandon her nuclear ambitions" and vowed to stand with European allies to pressure Tehran to do so.

WAR.WIRE