The White House said Wednesday that North Korea's nuclear initiative is a threat to world peace and urged the secretive regime in Pyongyang (search) to resume talks aimed at ending the program.

"North Korea's nuclear program and nuclear weapons programs and its past and continuing proliferation activities are a threat to global peace and security," White House press secretary Scott McClellan said. "North Korea's actions underscore the importance of moving forward through the six-party talks."

McClellan, however, would not comment on a published report that said that based on scientific testing, U.S. intelligence agencies and government scientists believe that North Korea sold processed uranium to Libya (search). He said he would not discuss intelligence matters.

McClellan urged North Korea to return to the six-party talks soon. He said two members of the National Security Council (search) staff recently traveled to several Asian capitals to discuss ways to restart the negotiations.

"We put forward a proposal at the last round of talks," he said. "We believe it addresses the concerns of all parties involved in those decisions. We believe that the proposal is the way forward to finding a peaceful, diplomatic solution to the nuclear issue in North Korea."

"The proposal and the six-party process is the best way for North Korea to address the concerns of the international community and to end its international isolation," he said.

According to a report in The New York Times Wednesday editions, the scientific finding supports earlier clues that the dictatorship exported fuel for atomic weapons.

Government officials in Washington are trying to determine whether North Korea has sold uranium, an ingredient necessary for atomic weapons, to other countries, including Iran and Syria. So far, there is no evidence of that.

The Times reported that international inspectors tested nearly two tons of uranium material that Libya surrendered to the United States last year when it dismantled its nuclear program. The material, uranium hexafluroide, can be converted into bomb fuel.

An unnamed official at the Oak Ridge National Laboratory (search) in Tennessee, where extensive testing was performed in recent months, told the Times, "with a certainty of 90 percent of better, this stuff's from North Korea."

Experts said the findings advance the West's understanding of North Korea's uranium program.

"It means the North Koreans have built a facility to process uranium," Leonard S. Specter, the deputy director of the Center for Nonproliferation Studies at the Monterey Institute in California, told the Times. "And it raises the disturbing prospect that they've now made enough of it to feel comfortable selling some."

Nuclear intelligence experts said they compared samples of the Libyan uranium with samples from other countries by matching uranium isotopes.

They concluded that the uranium had to have come from North Korea.