MANILA, Philippines, Jan 25, (AP): Chinese coast guard ships and a Chinese navy helicopter harassed a group of Philippine fisheries vessels conducting a scientific survey in a hotly disputed area of the South China Sea, forcing them to cancel the operation, the Philippine coast guard said Saturday. Beijing has repeatedly asserted sovereignty over most of the South China Sea and accused rival claimant states, including the Philippines, Vietnam and Malaysia of encroachment.

China has demarcated its territorial claims with a 10 dashed-line printed on maps but has not provided the exact coordinates. The harassment took place Friday near Sandy Cay, three small uninhabited sandbars flanked by an artificial island base of Chinese forces and a Philippines-occupied island in the Spratlys archipelago, the coast guard said.

The Chinese coast guard ships approached two larger vessels, which maneuvered to avoid a collision, and a navy helicopter flew low over two smaller boats deployed by the ships, forcing the survey to be called off. Videos released by the Philippine coast guard show a Chinese coast guard ship sailing very close to a vessel officials identified as belonging to the Philippines. Another video shows a Chinese military helicopter hovering low over the rough seas near a vessel flying a Philippine flag.

There was no immediate response from Chinese officials. The latest flare-out of the long-simmering territorial disputes in one of the world’s busiest trade and security passageways could test President Donald Trump’s commitment to maintain America’s role as a counterweight to China, which has increasingly carried out assertive actions in the disputed waters.

His predecessor, Joe Biden, strengthened an arc of security alliances in Asia while in office in a bid to curb China’s aggressive actions in the South China Sea, East China Sea and around Taiwan, a self-governed island which Beijing has vowed to take by force if necessary. Secretary of State Marco Rubio in a telephone call on Wednesday with his Philippine counterpart, Enrique Manalo, discussed issues of mutual concern, including "the People’s Republic of China’s dangerous and destabilizing actions in the South China Sea,” State Department spokesperson Tammy Bruce said.