Top American defence officials called North Korea's nuclear threat more lethal than ever even as an envoy from the Communist regime was headed Wednesday to the United States to discuss the issue.

'We do not today — nor will we ever — accept a North Korea with nuclear weapons.'—Robert Gates, U.S. defence secretary

U.S. Defence Secretary Robert Gates accused North Korea of attempting widespread nuclear proliferation.

"Everything they make they seem to be willing to sell," Gates told a group of American and South Korean troops at the U.S. military headquarters in central Seoul. "We do not today — nor will we ever — accept a North Korea with nuclear weapons."

In a separate interview in Seoul, the chief of the U.S. Pacific Command that oversees the region's military mission said North Korea "needs to be watched very closely."

However, Adm. Robert F. Willard also stressed diplomacy's role, calling North Korea "a whole-of-government problem."

North Korea's No. 2 nuclear negotiator, Ri Gun, was in Beijing on Wednesday on his way to the U.S., where he is scheduled to attend a security forum next week in California and a seminar in New York.

Ri also is reportedly expected to meet with the chief U.S. nuclear negotiator, Sung Kim, to set up bilateral talks.

Tensions high

The North is thought to have enough weapons-grade plutonium for at least half a dozen atomic bombs, and has sought to advance its long-range missile capabilities.

Tensions remain high after North Korea fired five short-range missiles off its east coast on Oct. 12. A day later, the country announced a no-sail zone in areas off the its east and west coasts for Oct. 10 to 20, an apparent signal it would carry out more missile tests.

At the same time, the North has reached out to Seoul and Washington, freeing detained American and South Korean citizens.

North Korean leader Kim Jong Il said earlier this month that his country could rejoin six-party nuclear talks, depending on the status of direct talks with the U.S.

With files from The Associated Press