A senior United States official is in East Asia for talks on the North Korean nuclear crisis.
John Bolton wants Pyongyang's neighbours to help resolve the crisis
John Bolton, US undersecretary of state for arms control and
international security, said on Monday that he had discussed the issue with leaders in Beijing, before heading to South Korea and Japan.
But hopes of an early resumption of talks between the US and North Korea appeared to fade when South Korea's Foreign Minister, Yoon Young-kwan, warned that consultations between the North and its closest ally China were slowing down.
Mr Yoon suggested that growing optimism that there might be negotiations with North Korea as early as next month may now be misplaced.
"The ball is in North Korea's court," Mr Yoon said.
Mr Bolton's visit is the latest in a series of diplomatic moves to try and resolve the crisis over North Korea's nuclear ambitions, which began last October.
The US wants the next round of talks to include countries like South Korea and Japan, arguing that Pyongyang's nuclear programme is an issue for the entire region.
But North Korea has previously signalled it would rather talk with Washington alone.
"I don't see we could be making progress by denying
participation by countries that have a legitimate stake in the
process," Mr Bolton said.
But he stressed that Washington was "flexible" on the format of talks, as long as it is multilateral.