"Talks are underway among countries concerned in order to have a working group meeting in August," Ban said in a speech at a seminar here.

"But it is hard to predict yet when (the working group meeting) will take place," he said.

His statement came amid confusion over Pyongyang's intentions after its official media appeared to be hinting North Korea might not attend the agreed-upon working group talks.

This meeting, whose timing and venue have not yet been fixed, is aimed at paving the way for a fourth round of the six-nation talks due in Beijing by the end of September to discuss ways to resolve the confrontation over North Korea's nuclear weapons programme.

"It is important to ensure that the fourth round of six-nation talks take place in September and tangible progress must be made there," Ban said.

A spokesman of North Korea's foreign ministry said on Monday the United States "has destroyed itself the foundation for the talks, making it impossible for the DPRK (North Korea) to go to the forthcoming meeting of the working group," citing a US "hostile" policy toward the communist state.

But the spokesman fell short of threatening that North Korea would scupper the preparatory meeting or the full-session talks, while saying Pyongyang would "make sustained efforts for the peaceful settlement" to the issue.

A third round of talks which brought together the United States, the two Koreas, China, Japan and Russia in Beijing in an effort to resolve the impasse ended in June without tangible progress.

The United States tabled a plan then giving Pyongyang three months to shut down and seal its nuclear weapons facilities in return for economic and diplomatic rewards and security guarantees.

But the North Korean spokesman said on Monday "a nuclear freeze is possible and it can lead to the dismantlement of the nuclear program only when the situation develops in the direction of the US dropping hostile acts against the DPRK."

"On the contrary, these acts are escalating," he said.

North Korea's official Korean Central News Agency on Wednesday said "it cannot but be strange" for North Korea to sit at the negotiating table with the United States, accusing Washington of ratcheting up its hostile policy.

Washington and China played down Pyongyang's statements on Monday.

The US State Department said it was proceeding with the assumption the "working group" meeting would go ahead as planned sometime before the end of next month.

Beijing appealed for calm Wednesday and said it was confident the six-nation talks remained on track despite indications from Pyongyang it may pull out.

WAR.WIRE