Speaking after returning from visit Beijing where he met with his Chinese counterpart Ban said, "The North should clarify its position on what it means exactly when it talks about a freeze and the extent of such a freeze."

North Korea has offered to freeze its nuclear facilities in return for concessions from the United States including its removal from the US blacklist of terrorism-sponsoring nations.

However, Ban said the offer would be "unacceptable" if North Korea's nuclear freeze means simply going back to a 1994 deal under which it agreed to mothball its facilities that could be used to produce nuclear weapons based on plutonium.

"It must be something more than the 1994 deal in Geneva. All nuclear-related facilities must be frozen," Ban said.

The 1994 Agreed Framework between the United States and North Korea unravelled after October 2002 when Washington presented North Korea with evidence that it was running a clandestine nuclear programme based on enriched uranium.

Ban returned home Tuesday after a three-day visit to Beijing where he was briefed by his Chinese counterpart Li Zhaoxing, following Li's return from Pyongyang where the Chinese diplomat held a rare 90-minute meeting with North Korean leader Kim Jong-Il.

Two rounds of six-nation talks bringing together the two Koreas, China, Japan, Russia and the United States have failed to narrow differences over a key US demand for the complete dismantling of Pyongyang's nuclear programs.

At the last meeting in February in Beijing, participants agreed to set up working groups ahead of new six-way talks scheduled to take place before the end of June.

Ban said the North Koreans had told Li that they would take part in planned working groups.

"North Korea's position is that the process for resolving the nuclear issue through six-nation talks should continue," Ban said, citing Li's briefing.

"North Korea is willing to take part in the working groups' meeting and wants the meeting to deal with its demand for rewards in return for a freeze," Ban said.

North Korea has made no proposal on when the working groups should meet, Ban said.

But Ban said he and Li were in agreement that the momentum of dialogue to resolve the nuclear impasse should be kept alive by ensuring that a third-round of six-way talks take place by the end of June as previously agreed.

WAR.WIRE