Iranian and U.N. nuclear officials began a new round of talks here on Monday, this time to probe the source of weapons-grade uranium that was found at Tehran's university, the official IRNA news agency reported.

It was not clear from the report how or when the weapons-grade uranium was discovered at the Technology faculty of the state university.

The meeting between the International Atomic Energy Agency delegation and its Iranian hosts comes in the wake of a surprising U.S. intelligence report last week that concluded Iran had stopped its nuclear weapons program in late 2003 and had not resumed it since.

The talks also follow an IAEA report last month which stated Iran had been generally truthful about its past uranium enrichment activities. Much of the 10-page report focused on Iran's black-market procurements and past development of uranium enrichment technology.

But the talks Monday were related to a separate issue -- the university find. It's believed this was the first time the incident was discussed.

The IAEA's mandate obliges it to investigate a country's nuclear activities and probe all suspicious findings, such as the traces at Tehran university.

In 2003 and 2004, the IAEA revealed other incidents where weapons-grade uranium was found elsewhere in the country, but Iran at the times said those traces came from imported equipment that had been contaminated before it was purchased.

The parts suspected of being contaminated in those incidents were believed to have come from Pakistan.

The IAEA delegation in Monday talks was headed by Herman Nackartes, head of the watchdog's Safeguard Operations department.

In its November report, the IAEA also said it requested access to documents, individuals and relevant equipment and locations for sample-taking to determine the source of the contamination.

Iran officials taking part in the talks must answer all IAEA questions about how the uranium particles got to the university.

While Iran has responded to many IAEA questions about past nuclear activities such as P-1 and P-2 centrifuges, a technology used to enrich uranium, some issues still remain unresolved, such as the university contamination.

Iran has also met a key IAEA demand and handed over long-sought blueprints on how to mold uranium metal into the shape of warheads which Tehran said were obtained from black market nuclear dealers.

The United States and some of its allies accuse Iran of seeking to build nuclear weapons but Tehran has denied the charges, saying its nuclear program is only geared toward generating electricity, not a nuclear bomb.

Iran maintains it would never give up its right under the Nuclear Nonproliferation Treaty to enrich uranium and produce nuclear fuel.