As two 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.

Amid efforts to convene a new round of six-nation talks to end the nuclear crisis, North Korea said it expected concessions in return from Washington.

The United States 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, the agency said in a dispatch monitored here.

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

But first, North Korea must agree to scrap its nuclear weapons programme, a demand rejected by Pyongyang as a US ploy to disarm the country prior to invasion.

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 US delegates headed for Pyongyang at the invitation of the Stalinist state.

Two non-government teams -- one of academics and a scientist, the other from Congress -- were to depart for Pyongyang from Beijing.

US congressional staffers Keith Luse and Frank Jannuzi lead one group while the other includes former State Department officials Jack Pritchard and Sig Hecker, a nuclear scientist who from 1985-1997 directed the Los Alamos National Laboratory where the atomic bomb was first developed.

Though neither group is government sponsored, delegates are likely to brief Washington on their return, the US embassy in Beijing said.

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.

A senior Russia diplomat who attended the initial round of talks said both sides were intransigent.

"The reasons are the same old ones -- mistrust and very high demands set by both sides," Russian Deputy Foreign Minister Alexander Losyukov told Interfax news agency after a meeting with senior Chinese officials on Monday.

South Korea's Foreign Minister Yoon Young-Kwan said Tuesday that a new round of talks would be "difficult" to arrange this month and could even be pushed back to the middle of the year as North Korea and the United States harden their positions.

"I hope the talks will be held in the first half of this year at the latest," South Korean Foreign Minister told journalists here.

North Korea, which said Monday the "ball is in the US court," retiterated Tuesday that propects for talks depended on Washington's "attitude.

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