US Defence Secretary Lloyd Austin shook hands with China’s Minister of National Defense Li Shangfu on the sidelines of a security summit in Singapore but the two did not have a “substantive exchange,” the Pentagon said on Friday.

In a video posted on Twitter by a Wall Street Journal reporter, Austin was seen smiling while shaking hands with Li around a dinner table. Reuters could not immediately verify the authenticity of the images.

In a statement, the Pentagon said the two spoke only briefly.

“The Department believes in maintaining open lines of military-to-military communication with the PRC — and will continue to seek meaningful military-to-military discussions at multiple levels to responsibly manage the relationship,” Pentagon spokesman Brigadier General Pat Ryder said, referring to China by its official name, the People’s Republic of China (PRC).

China earlier declined a formal meeting with Austin during the Shangri-La security summit taking place over the next few days.

Relations between China and the United States have been tense, with friction between the world’s two largest economies over everything from Taiwan and China’s human rights record to its military activity in the South China Sea.

Despite the tensions and heated rhetoric, US military officials have long sought to have open lines of communication with their Chinese counterparts to be able to mitigate potential flare-ups or deal with any accidents.