A group of US government experts and other international scientists has determined that traces of bomb-grade uranium found two years ago in Iran came from contaminated Pakistani equipment and are not evidence of a clandestine nuclear weapons program, the Washington Post reported Tuesday.

"The biggest smoking gun that everyone was waving is now eliminated with these conclusions," the Post quoted a senior official, who discussed the still-confidential findings on the condition of anonymity.

The existence of the group of experts had not been previously reported, the newspaper said, adding that they had met in secret to pore over data collected by inspectors from the International Atomic Energy Agency (IAEA).

The IAEA, according to Western diplomats, has already concluded that enriched uranium particles found in Iran were from smuggled Pakistani equipment.

Iran has long contended that the uranium traces were the result of contaminated equipment bought years ago from Pakistan. But the Bush administration had pointed to the material as evidence that Iran was making bomb-grade ingredients.

The State Department stressed Tuesday that the question about contamination was only "one part of this overall set of questions" about Iran's nuclear program.

"We believe that they are developing, they are pursuing a nuclear weapon -- that of course we would cooperate with the IAEA in their work and we would expect any other country to do so," department spokesman Sean McCormack told reporters.

Listing what he called "unresolved concerns" about Iran's nuclear program, he questioned Iran's so-called P-1 and P-2 centrifuge program and the extent of its dealings with alleged clandestine nuclear procurement networks.

"There are still questions separately about their pursuit of a plutonium route to a nuclear weapon, separate from the highly-enriched uranium route," McCormack said.

"There are questions about Iran's formerly secret uranium mine ... There are questions about whether Iran is still refusing to allow the IAEA further access to investigate suspicions about high explosives" at the Parchin military facility, he said.

McCormack asked why Iran was still refusing access to the IAEA to investigate several Iranian officials whom the agency believed might be involved in suspicious nuclear-related procurement.

He also raised IAEA's concerns about why Iran bulldozed a production facility to the ground before allowing the agency to visit the site.

In addition, McCormack highlighted IAEA concerns about the extent of the Iranian military's role in the country's nuclear program.

"These are all big questions that are still unresolved," he said.

The IAEA called on Iran earlier this month to resume a full suspension of nuclear fuel activities it had undertaken as a confidence-building measure for talks with the European Union on guaranteeing its atomic program was peaceful.

Washington was not part of the EU diplomatic initiative, but supported it.

The IAEA is to report September 3 on Iran's compliance, with the EU ready to take Tehran before the UN Security Council for possible sanctions if the suspension is not resumed.

Iran suspended nuclear activities last November but broke that suspension earlier this month as it rejected an EU offer of trade and other benefits, saying they failed to recognize the Islamic republic's rights under the nuclear Non-Proliferation Treaty to make nuclear fuel.

France, Britain and Germany, dubbed the EU-3, have called off a meeting with Iran on August 31 because of its decision to resume nuclear activities, the French foreign ministry said Tuesday.

McCormack said the talks should seek the "truth" about any Iranian weapons program.

"And at every turn, the Iranians obfuscate, they try to change the subject. The focus should be on Iran's behavior. That's why we're having this discussion."

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