NORTH Korea vowed to strengthen military ties with China on Wednesday, days after the North's leader Kim Jong-il finished a visit aimed at bolstering the bond with his isolated country's sole major supporter.

Comments from Kim Yong-nam, the second-ranked official in North Korea, highlighted the recent efforts of Pyongyang and Beijing to shore up their relationship in the face of regional tensions and possible succession moves in the North.

China confirmed on Monday that Kim Jong-il, who rarely leaves his country, visited for five days and told President Hu Jintao that he was willing to return to negotiations about scrapping the North's nuclear weapons.

Kim Yong-nam told a visiting commander of the Chinese People's Liberation Army (PLA) that the bond between the two neighbors has "shown great vitality," China's Xinhua news agency reported from Pyongyang.

Beijing has recently fretted about military exercises between the United States and South Korea, saying they threaten China's security interests and could destabilize the region.

On Wednesday, the PLA navy was due to start artillery exercises in the Yellow Sea between China and the Korean peninsula.

Washington and Seoul plan to hold their own military exercise in international waters off the west coast of the Korean peninsula, a move the Pentagon has said is meant to show North Korea that Washington is committed to defending ally South Korea.

The September 5-9 naval drills are aimed largely at detecting and repelling North Korean submarines from infiltrating the South's waters, a government official said.

The latest exercises follow Seoul's pledge to take tough action against the North in the event of further provocations, after it accused Pyongyang of a submarine attack against one of its navy ships in March, killing 46 sailors.

Kim Yong-nam told visiting PLA commander Zhang Youxia that their two countries' military forces should grow closer.

"In the future, North Korea will consolidate and develop exchanges and cooperation with China in every sphere, and make increasing efforts to strengthen friendly cooperation between our two militaries," he told Zhang, commander of the PLA's Shenyang military region, which adjoins North Korea, according to Xinhua.

Some foreign analysts believe Kim Jong-il may be seeking to line up China behind plans to install an heir apparent, possibly his son Kim Jong-un, at a rare political congress this month.

The bond between the two neighbors dates back to China's support for North Korean communists and its support for the North in the Korean War of 1950-1953.

Kim said their "traditional friendship has withstood the test of history and shown great vitality." Zhang met senior North Korean military leaders on Tuesday, said the report.

In 1961, Beijing and Pyongyang signed a treaty which calls for either to aid the other if attacked. It remains in force, but its potential application is ambiguous.