Hill insisted that North Korea give up its nuclear weapons, while Pyongyang stood firm that it would only disarm in return for concessions.

"I want to stress the ball is in their court. They know what they have to do," Hill told reporters on a brief stop in Japan as he flew between Beijing and Washington.

"We are not interested in having a situation in which they pretend to denuclearize and we pretend to believe them. They've got to denuclearize," he said.

North Korea on October 9 defiantly tested an atom bomb. But three weeks later it said it would return to six-way talks it had shunned for a year.

Hill met for two days in Beijing with his North Korean and Chinese counterparts on setting a date for the talks.

Envoys from South Korea and Japan also gathered in the Chinese capital to jump-start the roundtable negotiations, which involve Russia as well.

Hill said much of the discussion focused on implementing a September 19, 2005 deal, under which North Korea agreed in principle to give up its nuclear program in exchange for aid and security guarantees.

North Korea launched a boycott of the talks two months after the September agreement to protest a set of US financial sanctions.

In Beijing, North Korean negotiator Kim Kye-gwan said North Korea had agreed to return to talks because the nuclear test strengthened its position. Kim said Pyongyang would not give up nuclear weapons without concessions in return.

"There are many commitments in the September 19 joint statement and at this stage, there won't be any unilateral abandonment" of nuclear weapons, Kim said.

The latest crisis began when the administration of US President George W. Bush, who famously branded North Korea part of an "axis of evil", accused the regime of secretly producing nuclear bombs.

North Korea kicked out inspectors from the International Atomic Energy Agency (IAEA) in 2002 as tensions built up.

On a visit to Tokyo, IAEA chief Mohamed ElBaradei said the UN nuclear watchdog was ready to go back into North Korea if the six-party talks reached a deal.

IAEA involvement would help "assure the international community that all nuclear activities in the DPRK (North Korea) are exclusively for peaceful purposes," he said.

While condemning North Korea's nuclear test, ElBaradei said it showed the need "to engage in an immediate and sustained dialogue to address such a situation and its underlying causes".

The Bush administration has refused to talk to North Korea bilaterally, except on the sidelines of six-nation talks. Hill said the US was only interested in negotiations that could yield an agreement.

He said he had asked Kim Kye-Gwan during their two days of talks for any new ideas on breaking the impasse.

"Unfortunately he did not have anything new, but I told him to take his time and if he could think of some, we'd be happy to consider them," Hill said.

"The problem is not setting the date," he added. "The problem is getting to the talks and making progress because the purpose of the talks is not (just) to talk."

China, which has faced pressure to show its influence over its fellow communist country, said Thursday the meetings it hosted were "meaningful and increased mutual understanding".

Japan also played down the failure to set a date.

"There is no reason to be so pessimistic about it. The content is more important" than the schedule, said Chief Cabinet Secretary Yasuhisa Shiozaki, the government spokesman.

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