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 favoured 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 travelled 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.