Traces of enriched uranium discovered on recently surrendered Libyan nuclear components appear to have come from Pakistan, a critical black-market supply hub that also made deliveries to Iran and North Korea, U.N. inspectors reported yesterday in Vienna.

The news may prove less significant to Libya than to Iran, which has said that uranium traces on its gas centrifuges also came from its distant supplier and are not proof of an ongoing weapons program.

The International Atomic Energy Agency's latest report concludes that Libya, which agreed in December to surrender its nuclear efforts, is cooperating but must provide more information and evidence before it can be declared clean.

Libya has "done more or less what they've been asked to do," but its cooperation has been "less than perfect," said a well-informed Vienna diplomat.

Some aspects of Libya's nuclear activities are "explained and well documented," while a study of other matters suffers from a lack of documentation, according to the report, which provides updates on the IAEA's effort to understand Libya's clandestine efforts. Central to the inquiry is the source of uranium contamination -- high enriched and low enriched -- found on gas centrifuge equipment.

IAEA inspectors have been tracking Libya's abortive experience with gas centrifuges in the early 1980s as well as its return to the technology in the late 1990s with supplies and tutelage provided by the network headed by Pakistani scientist Abdul Qadeer Khan.

Two generations of centrifuges that originated in Pakistan were found with traces of uranium. Tests on the early centrifuges contained traces comparable to those found in Pakistan itself, the report said.

Similarly, traces were discovered on the more advanced parts found by IAEA inspectors in unopened boxes in January 2004. The inspectors said the evidence tended to confirm Libya's assertion that the contamination occurred before the components reached Libya and that they had not been further assembled or tested there.

Iran made a similar argument earlier this year when the IAEA discovered uranium traces on equipment imported from Pakistan through the Khan network. But the U.N. agency has said it discovered different types of contamination on Iranian components produced in Iran and those imported from Pakistan. That suggested to some scientists that Iran may have enriched uranium on its own.

The IAEA's findings in Libya, said the Vienna diplomat, "don't necessarily mean we believe Iran's story."

The IAEA is negotiating with Pakistan to take samples from nuclear equipment and facilities to better assess the Libyan and Iranian claims. The diplomacy is delicate because Pakistan opted out of the nuclear Non-Proliferation Treaty and wants nothing that could be construed as a precedent for international inspection.