"North Korea's nuclear programs and nuclear weapons programs and its past and continuing proliferation activities are a threat to global peace and security," said spokesman Scott McClellan.

But McClellan refused to comment specifically on a news report that the Stalinist regime almost certainly sold processed uranium to Libya, according to US tests conducted on nuclear material surrendered by Libya last year.

"I will not get into discussing matters of intelligence," he said after The New York Times report, which cited anonymous US officials familiar with US intelligence.

The determination, included in a classified briefing distributed recently to top US officials, has triggered an investigation to see if North Korea has also sold uranium to other countries, including Syria and Iran, the Times said.

US President George W. Bush was to say in his annual State of the Union address later in the day that he favored using six-nation talks with North Korea as the way to achieve a peaceful resolution to the nuclear dispute.

"We would urge North Korea to return to the six-party talks soon," McClellan said, calling them "the best way for North Korea to address the concerns of the international community and to end its international isolation."

McClellan confirmed that two senior officials from Bush's national security council traveled to Japan, China, and South Korea to discuss how to restart the six-part talks, which also group North Korea, Russia, and the United States.

"They're also discussing a wide range of regional and international issues that relate to our goals of peace and stability in Asia and around the world," he said.

It was unclear how the information in the Times report would alter the debate about assessing the North Korean nuclear threat.

North Korea has attended three rounds of inconclusive discussions on the nuclear stand-off and shunned a fourth round originally scheduled for last September.

A recently retired Pentagon official experienced in dealing with Pyongyang told the daily the finding was "huge, because it changes the whole equation with the North."

"It suggests we don't have time to sit around and wait for the outcome of negotiations," said the unidentified former official. "It's a scary conclusion because you don't know who else they may have sold to."

The tests at Oak Ridge National Laboratory, US state of Tennessee, concluded that samples of uranium surrendered by Tripoli when it dismantled its nuclear program did not come from Pakistan or other countries suspected of exporting nuclear technology, intelligence officials said.

By a process of elimination, one official said that "with a certainty of 90 percent or better, this stuff's from North Korea."

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