The Philippines announced on Saturday the suspension of a scientific survey in the South China Sea due to “harassment” and aggressive actions from China’s coast guard and navy towards its fisheries vessels.

Manila and Beijing have experienced a series of escalating tensions in the contested waters of the South China Sea. China asserts its claim over nearly the entire strategic waterway, which facilitates $3 trillion in annual trade, overlapping with the claims of the Philippines, Indonesia, Malaysia, and Vietnam.

On Friday, two vessels from the Philippine Bureau of Fisheries, en route to collect sand samples from Sandy Cay near the Philippine-controlled Thitu Island, faced “aggressive maneuvers” from three Chinese Coast Guard ships, according to a statement from the Philippine Coast Guard.

The Philippine Coast Guard reported that four small Chinese boats were deployed to “harass” two rigid hull inflatable boats sent by the fisheries bureau to transport personnel to Sandy Cay. Additionally, a Chinese navy helicopter was observed hovering at an “unsafe altitude” over these vessels.

The Philippine Coast Guard stated that the survey operations were halted “due to this ongoing harassment and the lack of regard for safety demonstrated by the Chinese maritime forces.” The Chinese embassy in Manila has not yet responded to a request for comment. During discussions on January 16, Manila and Beijing agreed to seek common ground and explore avenues for cooperation despite their ongoing disputes in the South China Sea.