Manila, 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 planked 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.

Rubio “conveyed that the PRC's behavior undermines regional peace and stability and is inconsistent with international law,” Bruce said in a readout of the call.

Rubio “underscored the United States' ironclad commitments to the Philippines under our Mutual Defense Treaty,” Bruce said.

Biden and his administration had repeatedly warned China that the U.S. is obligated to help defend the Philippines, its oldest treaty ally in Asia, if Filipino forces, ships and aircraft come under armed attack including in the South China Sea. China has warned the U.S. to stay away from what it says is a purely Asian dispute.

In 2017, China accused the Philippine military of secretly plotting to occupy and build a structure on one of the three sandbars, about 2.5 nautical miles (4.6 kilometers) from the Philippine-occupied Thitu Island, two senior Philippine officials told The Associated Press at the time.

China protested and surrounded the sandbars with three navy ships, a coast guard ship and 10 suspected militia ships, according to a confidential Philippine government security report seen by the AP at the time.

Chinese and Philippine diplomats resolved the issue by agreeing that forces from both sides should not set foot on the sandbars, the two Philippine officials said.

Chinese ships, however, have continuously kept watch off the sandbars since then, according to the Philippine military.

Separately, the Philippine coast guard said it has been ordering Chinese coast guard ships to stay away from the Scarborough Shoal, another disputed area about 124 nautical miles (230 kilometers) off the northwestern Philippines.

The Chinese coast guard ships have approached up to 60 nautical miles (111 kilometers) from the Philippines coast in recent weeks, well within the country's exclusive economic zone, a stretch of water where a coastal state has exclusive rights to tap resources, but where foreign ships have rights of “innocent passage” as provided under the UN Convention on the Law of the Sea, the Philippine coast guard said.

The Chinese coast guard has defied the Philippine coast guard order to leave the area, which it said falls within Chinese waters. It warned the Philippines “to immediately stop all infringement activities, provocations and false accusations.” (AP) NSA NSA