Keeping the Korean Peninsula nuclear free is the "biggest challenge" facing China-U.S. relations in the coming years, the outgoing U.S. ambassador to China said Thursday. 

"One of the biggest challenges we face is that, President Barack) Obama and Vice President (Joe) Biden and Chinese leaders have talked a lot about, is trying to make sure the Korean Peninsula (is) nuclear free," U.S. Ambassador Gary Locke said at a farewell press conference. 

Other significant challenges facing the U.S. and China are on working together to bring peace and stability to Afghanistan. 

Earlier this month, U.S. Secretary of State John Kerry held meetings in Beijing with Chinese leaders, including President Xi Jinping, and told that China was prepared to take further punitive steps against North Korea unless the North denuclearizes itself through dialogue. 

China is asking the U.S. and other concerned parties to resume the denuclearization talks with North Korea, but Washington has insisted that Pyongyang should first prove with action its sincerity about disarming.

The six-party dialogue, which involves the two Koreas, China, the U.S., Japan and Russia, has been suspended since late 2008. 

Locke, who leaves Beijing later this week and will be replaced by former Montana Senator Max Baucus, also urged China and Japan to resolve territorial disputes through dialogue. 

"Of course, the United States takes no position on the ultimate sovereignty of those islets," Locke said. 

"But the United States simply wants that China and Japan could resolve this diplomatically and in a very peaceful, common and deliberate fashion," Locke said. "We call on both sides to avoid any types of actions that would deem provocative and raise tensions."  (Yonhap)