The top U.S. envoy on North Korea issues is in China to discuss pending bilateral matters.

Diplomatic sources in Seoul say Assistant State Secretary James Kelly's talks with Chinese officials will include discussions on the resumption of a new round of six-way talks on North Korea's nuclear standoff.

Kelly arrived in Beijing on Sunday just hours after reports of a huge explosion on North Korean soil.

Kelly's visit to China also comes after his meetings in Tokyo Friday with South Korean and Japanese counterparts on preparations for six-way talks aimed at persuading Pyongyang to abandon its nuclear ambitions.

A Japanese foreign ministry official told reporters after Friday's meeting that they had confirmed the importance of holding the fourth round of six-way talks in September as agreed on at the third round of atomic negotiations.