Updated

The U.N. nuclear watchdog agency has traced some particles of enriched uranium (search) found in Iran to Pakistan but has not yet verified Tehran's claims that all such material came into the country on equipment bought on the black market, diplomats said Tuesday.

Still, the reported finding boosts Iran's stance that it did not process uranium into its enriched form, which can be used both as fuel to generate power or as the core of nuclear warheads. It also weakens the case being built by the United States and its allies accusing the Islamic Republic of past covert enrichment as part of a clandestine weapons program.

Iran's contention that all traces of enriched uranium came into the country on "contaminated" black market equipment has been the focus of months of investigations by the International Atomic Energy Agency (search) as it tries to determine whether the Islamic Republic violated the Nuclear Nonproliferation Treaty (search).

Faced with evidence, Iran over the past year has acknowledged clandestinely assembling a centrifuge program to enrich uranium for what it says are plans to produce electricity but has denied actually embarking on the process.

The enrichment process spins uranium hexaflouride gas through thousands of centrifuges in series to gain increasingly higher levels of a uranium compound that can reach weapons grade above 90 percent.

The International Atomic Energy Agency refused to comment Tuesday. IAEA spokeswoman Melissa Fleming said no new findings of the agency would be made public ahead of a report being prepared for a Sept. 13 meeting of the agency's board of governors.

The report, being written by IAEA Director General Mohamed ElBaradei (search), will review the agency's progress in answering questions about nearly two decades of secret nuclear activities by Iran first revealed in 2003.

Most of the concerns focus on the sources of traces of highly enriched uranium found at several sites in Iran, and the extent and nature of work on the advanced P-2 centrifuge, used to enrich uranium.

The United States and its allies argue that Iran's clandestine activities included covert uranium enrichment — which, when undeclared, is a violation of the Nonproliferation Treaty.

The diplomats, who spoke to The Associated Press on condition of anonymity, said the agency had only been able to conclusively link one sample — particles enriched to 54 percent — found at one Iranian site to Pakistan, although another sampling enriched to a lower degree might also have come on equipment bought from the network headed by Pakistani scientist Abdul Qadeer Khan.

They said the findings strengthened Iran's hand ahead of the September meeting, but that the agency still was far from establishing the origin of all traces of enriched uranium found in Iran — and that it may never be able to do so.

The diplomats, who are familiar with Iran's nuclear dossier, said lack of clarity on that issue as well as Tehran's past cover-ups, its spotty record of cooperation with the IAEA investigation and its insistence on the right to enrich uranium still keep it in the IAEA spotlight.

"It's a boost for Tehran," said one of the diplomats of the enriched uranium finding. "But there are other things it still needs to worry about."

Iran's continued insistence on its right to enrich uranium and other demands have caused strains with France, Britain and Germany, which had hoped to convince it to scrap such plans. On Monday, diplomats said that Iran told the three that it wants them to back its right to "dual use" nuclear technology, which can have peaceful and weapons applications.