Supplied by the worldwide black market, Libya processed a small amount of plutonium in a nuclear weapons program that remained undetected for 20 years until Tripoli went public with its efforts, the U.N. atomic watchdog agency said Friday.

Citing a confidential report from the International Atomic Energy Agency (search), diplomats said Libya separated grams of the substance, much less than the nearly 7 pounds required to make a nuclear bomb.

Still, the revelation appeared to reflect a nuclear arms program that was substantially more advanced than the agency initially estimated.

IAEA Director General Mohamed ElBaradei (search) prepared the 10-page report ahead of an agency board of governors' meeting next month, and diplomats shared it with The Associated Press.

Libya announced in December it sought to develop weapons of mass destruction and promised to scrap its research programs. It was one of several moves by Muammar al-Qaddafi (search) to end Libya's international isolation and shed its image as a rogue nation.

American and British intelligence agencies spoke of a fairly advanced nuclear program, but the IAEA initially described it as being at the beginning stages.

The report said Libya "imported nuclear material and conducted a wide variety of nuclear activities which it had failed to report" to the IAEA as required by agreements with the agency, diplomats said. Those imports included centrifuges, which are machines that can be used to enrich uranium for nuclear weapons or nuclear power.

Much of Libya's efforts focused on enriching uranium, the report said. That -- along with producing plutonium -- is one way to develop the nuclear material used in warheads.

David Albright, a former nuclear weapons inspector in Iraq who now runs the Institute for Science and International Security (search) in Washington, said the plutonium appeared to be a sideline, with the Libyans clearly more interested in enriching uranium to weapons grade.

"The main story in Libya is the centrifuge plant," Albright said.

From the early 1980s through 2003, "Libya imported nuclear material and conducted a wide variety of (clandestine) nuclear activities," the report said.

For example, Libya failed to declare imports of uranium compound UF6, which is used in the enrichment process, in 1985, 2000 and 2001, the report said.

A Sri Lankan businessman, Bukhary Syed Abu Tahir, who is implicated in the nuclear black market, says a Pakistani scientist told him of UF6 shipments to Libya. That scientist, Abdul Qaheer Khan, led an illicit network supplying nuclear technology to rogue nations such as Libya, Iran and North Korea.

According to Tahir's account to Malaysian police, Libya approached Khan in 1997 for help building a uranium enrichment program.

Around 2001, Khan told Tahir that "a certain amount" of enriched uranium was flown from Pakistan to Libya, the Malaysian report said. Subsequently, centrifuge units arrived in Libya from Pakistan.

What Khan's network could not get for Libya directly, it helped the country build, sending machines and technicians to set up centrifuge-making operations and calling it "Project Machine Shop 1001," according to Tahir's account.

The IAEA report, in its comments on the black market, alluded to Khan and his associates without naming them.

"It is evident already that a network has existed whereas actual technological know-how originates from one source, while the delivery of equipment and some of the materials have taken place through intermediaries who have played a coordinating role," the report said.

These middlemen then subcontracted the manufacturing "to entities in yet other countries," the report said.

After its December disclosure, Libya surrendered drawings of a nuclear warhead to American and British experts. The blueprints and accompanying documents now are in the United States under IAEA seal.

Diplomats recently told the AP that the drawing detailed how to build a warhead for a large ballistic missile, using technology developed by the Chinese in the 1960s that triggers a nuclear blast by a small conventional explosion.

In its comments on the drawings, the report said only that Libya acknowledged receiving "documentation related to nuclear weapons design and fabrication from a foreign source."