U.S. says it has solid evidence of a nuclear black market.

The Bush administration can ``scientifically prove'' Libya acquired North Korean uranium through the nuclear black market that a Pakistani scientist helped set up, according to high-level sources.

Japanese officials were informed of this in January by Michael Green, senior director for Asia on the White House National Security Council, the sources said.

They said he passed along the U.S. intelligence to Chief Cabinet Secretary Hiroyuki Hosoda and high-ranking Foreign Ministry officials.

Green, according to the sources, said the United States can show that North Korean uranium was transported to Libya via the nuclear black market that Pakistani nuclear scientist Abdul Qadeer Khan helped establish.

Green said the White House remains committed to trying to seek a peaceful resolution of the North Korean nuclear weapons issue through six-nation talks.

The sources said Green explained that North Korea sold uranium hexafluoride, used in uranium enrichment, to Libya.

The illegal trade came to light after Libya announced it was abandoning its nuclear weapons program. Its dismantled facilities and materials were removed from Libya and shipped to the United States to be analyzed. It was then that U.S. researchers determined that processed natural uranium used by Libya originated in North Korea.

Green called North Korea's activities a violation of the 1994 Agreed Framework that Pyongyang signed with the United States.

A report by the International Atomic Energy Agency noted that Libya was said to have purchased about 1.7 tons of uranium hexafluoride in 2000 and 2001 from ``a certain nation.''

``Intelligence about trade in nuclear materials by North Korea had until now been mainly based on eyewitness accounts or documentary evidence,'' said a Japanese government source. ``It is highly significant that a scientific rationale has been established for the proliferation of materials that can be used in weapons of mass destruction.''

However, not all experts agree it can be definitively stated that the uranium came from North Korea. They said the United States might have concluded the uranium sold to Libya had come from North Korea through a process of elimination. After determining that the uranium did not match yellowcake mined elsewhere in the world, they might have concluded the only possible source was North Korea.

They noted that there is no firm evidence linking the transport of uranium from North Korea via Pakistan. In this context, they cited U.S. assertions of Iraq possessing weapons of mass destruction that eventually proved to be false. Thus, they called for greater care in jumping to conclusions about the source of weapons-grade materials.

If North Korea is found to be involved in the nuclear black market, the Bush administration will be obliged to consider additional measures to rein in Pyongyang's nuclear ambitions, sources said.

Khan admitted to the black market's existence in February 2004. After he was temporarily detained by Pakistani authorities, some American officials assumed the black market had been effectively shut down.

However, the new information provided by Washington indicates the network that Khan helped create may be far more complex than originally thought.

U.S. sources told The Asahi Shimbun that Khan handed over a list of suppliers in the nuclear black market to North Korea. Pyongyang might have used that list to export uranium to Libya.(IHT/Asahi: March 7,2005)