The two communist countries are locked in a long-standing territorial dispute over the Paracel and Spratly islands in the South China Sea.

Vietnam’s premier is due to return home Wednesday after attending a summit hosted by the United States aimed at bolstering regional resolve in the face of China’s military muscle-flexing.

On Wednesday, Beijing defended the deployment of armaments in the South China Sea after Taiwan said surface-to-air missiles had been installed on a disputed island in the Paracel chain in the region.

In a pre-planned event, more than 100 people gathered in Hanoi to mark an older territorial conflict: China’s 1979 invasion of Vietnam’s northernmost provinces.

Security officials stood by as veterans chanted “down with China, down with China’s invasion.”

Thirty seven years ago, 600,000 Chinese troops invaded northern Vietnam to “teach Vietnam a lesson” for ousting the Beijing-backed Khmer Rouge in Cambodia. China withdrew its troops after a month, but both powers claimed victory.

Although Vietnam fetes its military victories over the French and American armies, it did not arrange any official events to mark the China border war - much to the chagrin of veterans and activists.

“We are very sad that there has never been any official organisation (memorial) for the day,” 64-year-old Vietnamese war veteran Pham Thanh said at Wednesday’s commemoration in central Hanoi, where demonstrators carried banners that read “we will never forget”.

Beijing’s increasingly assertive stance in contested waters has triggered public anger and rounds of protests in authoritarian Vietnam where the demonstrations are sometimes forcefully broken up.

China is also Vietnam’s largest trading partner, complicating Hanoi’s position towards its neighbour.

On Tuesday, US President Barack Obama announced plans to make his first state visit to Vietnam in May, which Vietnam’s foreign ministry hailed as “carrying Vietnam-US relations to new heights”.

Agence France Presse - February 17, 2016