Senior diplomats from the three countries met for two hours in Tokyo to prepare for the talks aimed at persuading Pyongyang to abandon its nuclear ambitions, he said.

"They confirmed the importance of holding the fourth round of six-way talks in September as agreed upon at the third round of talks," the Japanese foreign ministry official told reporters.

The meeting brought together Mitoji Yabunaka, head of the Japanese foreign ministry's Asian and Oceanian affairs bureau, South Korean Deputy Foreign Minister Lee Soo-Hyuck and US Assistant Secretary of State for East Asia and Pacific affairs James Kelly.

On the South Korean nuclear issue, the official said: "They shared the view that it should have no direct impact on the six-way talks."

Japanese and US officials praised Seoul's cooperation with the International Atomic Energy Agency on the issue, the official said.

Seoul admitted Thursday that its scientists had extracted a small amount of plutonium, a key ingredient for making nuclear bombs, in secret research in the early 1980s.

The admission came just a week after South Korea said its scientists had conducted unauthorised experiments to enrich uranium, which is also used to build atomic weapons.

At the previous six-party talks in June, the two Koreas, the United States, China, Russia and Japan agreed to meet again in Beijing by the end of September.

North Korea has since adopted a more belligerent tone toward the United States and South Korea while expressing doubts about the value of attending further discussions.

Earlier Friday South Korean Foreign Minister Ban Ki-Moon said in a radio interview that he could not be optimistic about the prospects for holding six-way talks this month.

A high-ranking Chinese delegation led by Li Changchun, a top Chinese Communist Party leader, arrived in North Korea Friday in a last-ditch effort to get Pyongyang's agreement to attend a fourth meeting.

The Japanese official said Tokyo pinned high hopes on the Chinese mission.

"We believe a full utilisation of this opportunity by China will be very important to make progress on the issue and holding the fourth round of talks early, especially by the end of September as earlier agreed," he said.

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