"It is difficult in reality to open the second round of talks within this year," Yoon told journalists during a regular weekly briefing.

The remark followed weeks of feverish diplomatic efforts to resume the six-nation talks by the end of this year, preferably from December 17 to 19.

Yoon, who until now has generally been upbeat on prospects for talks this year, did not specify a possible date for the next round.

"Consultations among countries concerned are still under way. ... We will work to open the nuclear talks as early as possible through cooperation with the United States and Japan, close consultations with China and Russia, and inter-Korean dialogue channels," he said.

The United States, China, Russia, Japan and the two Koreas held a first round of talks in Beijing in August, but failed to end the crisis that erupted in October last year when Washington accused Pyongyang of running an enriched uranium program in violation of a 1994 nuclear freeze accord.

But Yoon said he remained "not pessimistic" about resuming the second round of talks.

There have been wide US-North Korean differences over a draft statement to be adopted at the second round, according to media reports in Seoul and Tokyo.

North Korea has demanded a legally binding security guarantee from the United States in return for abandoning its nuclear ambitions. Washington wants the nuclear program scrapped first.

WAR.WIRE