A leading US nuclear envoy has called for "the unity and cooperation" of all parties to advance the denuclearization of the Korean Peninsula.

"We have always emphasized the importance of five-party unity and compared notes with Chinese colleagues," said Kim Sung, US special representative for the Democratic People's Republic on Korea policy, in Beijing.

"The Chinese agree that pressure has to be an important part of our approach on Pyongyang," Kim said on Friday before concluding his four-day trip to Seoul and Beijing.

Chinese Foreign Ministry spokeswoman Hua Chunying said the Korean nuclear issue is complicated and the concerns of relevant parties need to be addressed through dialogue and negotiation.

During his visit, Kim held "productive consultations" with Chinese counterpart Wu Dawei. He said he expects Beijing and Washington to have "in-depth, substantive discussions" over denuclearization on the Korean Peninsula during Chinese President Xi Jinping’s state visit to the US in September.

On Wednesday, a trilateral meeting between the US, Japan and the ROK was held in Seoul and reinforced pressure and sanctions on Pyongyang while keeping diplomatic options on the table.

China, the US, Russia, Japan, the ROK and the DPRK initiated rounds of six-party talks in Beijing in 2003 but negotiations have been stalled since December 2008.