The International Atomic Energy Agency is planning further investigation into Libya's nuclear weapons program, following the discovery of weapons-grade uranium on centrifuges.

An IAEA internal report says traces of highly-enriched, weapons-grade uranium have been found on equipment in Libya, similar to traces found last year in Iran.

Experts say the equipment was made in Pakistan, but a number of sources could be involved in selling nuclear equipment and know-how, including countries of the former Soviet Union, North Korea and South Africa.

The IAEA says it must dig deeper into the nuclear black-market headed by top Pakistani scientist Abdul Quadeer Khan, to find out what countries got hold of nuclear technology, and if terrorist groups were among the buyers.

The head of the IAEA, Mohamed ElBaradei, told reporters earlier this week in Vienna that there is a sophisticated network of terrorists, who have an interest in acquiring nuclear technology. He said, since the terrorist attacks on New York City in September 2001, the writing has been on the wall.

Rebecca Johnson, the editor of Disarmament Diplomacy, says, to unlock the secrets of the black market in nuclear technology, much more needs to be known about the Khan network.

"We have to understand that this A. Q. Khan network has been going on for not just a few years, but decades," she said. "It's really been going on for between 15 and 20 years now. This was part of how Pakistan supplied and funded its program. It did quid pro quos with others. The West, there's been suspicion about this for a long time in the academic community. My suspicion is that there were those in the West who knew about it at a much earlier stage."

IAEA inspectors are examining similarities between Iran's and Libya's nuclear programs, both of which reportedly have found supplies on the black market run by the Khan network. While Libya is co-operating with U.N. officials in tracing nuclear suppliers and buyers, both Iran and Pakistan are less willing to allow inspectors take samples for analysis.

Iran denies U.S. charges that it maintains a secret nuclear weapons program. The IAEA is trying to determine whether Iran's claim that it imported equipment contaminated with enriched uranium from Pakistan is true, or whether Tehran is working on a nuclear bomb.

The IAEA internal report disclosing the finding of weapons-grade uranium in Libya will be put on the agenda of the organization's 35-member board of governors' meeting, which opens in Vienna June 14.