Sullivan arrived in Beijing on Tuesday, the first US National Security Advisor to visit China since 2016, for three days of talks with Foreign Minister Wang Yi and other high-ranking officials.

The visit came as China became embroiled in security rows with US allies Japan and the Philippines. 

On Thursday morning, Sullivan met with senior Chinese army chief Zhang Youxia at the Beijing headquarters of the Central Military Commission.

"It's rare that we have the opportunity to have this kind of exchange," Sullivan told Zhang in opening remarks.

"Given the state of the world and the need for us to responsibly manage the US-China relationship, I think this is a very important meeting."

He said he hoped for "productive discussions" on "issues of mutual interest". 

Zhang, in turn, thanked Sullivan for his visit and said the meeting "demonstrates the value the US government puts on military security".

On Wednesday, Sullivan and Foreign Minister Wang discussed plans for their leaders to talk in the coming weeks -- and clashed over China's increasingly assertive approach in disputed maritime regions.

Sullivan "reaffirmed the United States' commitment to defending its Indo-Pacific allies", the White House said.

He also "expressed concern about [China's] destabilizing actions against lawful Philippine maritime operations" in the disputed South China Sea, it said.

Chinese state media reported that Wang issued his own warning to Washington.

"The United States must not use bilateral treaties as an excuse to undermine China's sovereignty and territorial integrity, nor should it support or condone the Philippines' actions of infringement," Wang told Sullivan, according to state broadcaster CCTV.

Wang and Sullivan previously met five times over the past year and a half -- in Washington, Vienna, Malta and Bangkok, as well as alongside Biden and Xi in Woodside, California in November 2023.

During their latest encounter, they also discussed the tense issue of Taiwan, the self-governing democracy that China claims.

China has kept up its sabre-rattling since the inauguration this year of President Lai Ching-te, whose party emphasises Taiwan's separate identity.

Wang stressed that Taiwan belonged to Beijing and that China would "certainly be unified", adding that the United States should stop arming Taiwan, according to CCTV.

The White House said Sullivan "underscored the importance of maintaining peace and stability across the Taiwan Strait."

The US and Chinese officials also discussed issues including Ukraine, the Middle East and the Korean Peninsula, both sides said.