"This is an interesting step on their part, a positive step, and we hope that it will allow us to move more rapidly to six-party framework talks," Powell told reporters.

"I am encouraged, I am encouraged by the statement the North Koreans made," he said.

North Korea offered earlier to refrain from testing and producing nuclear weapons in what it said was a "bold concession" to the United States aimed at ending the nuclear crisis.

As two unofficial US delegations headed for Pyongyang for a tour billed to include a rare visit to North Korea's Yongbyon nuclear complex, the Stalinist state spelled out its proposal for a nuclear freeze.

North Korea "is set to refrain from test and production of nuclear weapons and stop even operating nuclear power industry for a peaceful purpose as first-phase measures of the package solution. This cannot but be one more bold concession," Pyongyang's official Korean Central News Agency said.

Powell put a positive spin on the delay in convening a new round of six-nation crisis talks, first pencilled in for December, but according to Japanese and South Korean officials could now slip back to next month at the earliest.

"Because we're not sitting at a table, does not mean we have not been talking to each other, and a lot of papers have gone back and forth," he said.

"We are in touch with our four partners in this effort and some of our partners are directly in touch with North Korea. So we've been doing a lot."

The United States has demanded an irrevocable and verifiable decision by North Korea to abandon its quest for nuclear weapons.

On Monday it warned the Stalinist state that it could expect no rewards from Washington just for showing up at talks, also involving China, Russia, South Korea and Japan.

One potential stumbling block is that North Korea's offer included a condition that Washington would deliver "simultaneous" actions including removing North Korea from a State Department list of countries accused of sponsoring terrorism, lifting sanctions and resuming energy aid.

Washington has rejected North Korea's plan for "simultaneous" measures and maintains that it is only willing to discuss "sequencing" of steps to aid Pyongyang at the six-nation talks, not before them.

South Korean government officials said the latest proposal from Pyongyang appeared to contain nothing new but signalled North Korea's desire for dialogue.

Another signal from North Korea came as members of an unofficial US delegation arrived in Pyongyang at the invitation of the Stalinist state.

The team included a former US official who dealt with North Korea policy, a scientist and a top academic.

Another delegation, from Congress, was also heading for Pyongyang.

Efforts to reconvene nuclear crisis talks following the inconclusive first round in Beijing last August have so far failed with Washington accusing North Korea of setting preconditions and Pyongyang saying the United States is time-wasting and refusing to consider its proposals.

WAR.WIRE