Chinese coast guard ships backed by a military helicopter attempted unsuccessfully to block two Philippine government vessels carrying scientists from reaching two sandbars in the disputed South China Sea, Philippine officials said Friday.

Chinese coast guard personnel blew the horn on one of their ships for half an hour and repeatedly transmitted radio warnings during the confrontation Thursday, but the Filipino scientists managed to complete their four-hour marine and biodiversity research at the barren sandbars called Sandy Cay, the officials said.

The Chinese coast guard gave a different account of the faceoff. A spokesperson, Gan Yu, said in a statement that its law enforcement officers "boarded" the sandbars, which Beijing calls Tiexian Reef, and dealt with what it called "illegal activities" by 34 Philippine personnel who "ignored China’s warnings and dissuasion."

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"That’s another lie coming from the Chinese coast guard," Philippine coast guard Commodore Jay Tarriela said at a news conference on Friday. "For four hours, our marine scientists were able to continue their research."

Journalists who were invited to join the research mission witnessed the incident, Tarriela said.

chinese coast guard philippines

Seen above is a Chinese coast guard ship that is attempting to block a Philippine government vessel in a photo provided by the Philippine Coast Guard on March 21, 2024. The Philippine vessel contained scientists who were attempting to do marine research on two barren sandbars called Sandy Cay in the South China Sea.  (Philippine Coast Guard via AP)

It was the latest flareup in increasingly tense territorial disputes that are seen as a potential Asian flashpoint that might bring China and the United States into a conflict if they degenerate into a major armed confrontation.

China, the Philippines, Vietnam, Malaysia, Taiwan and Brunei have overlapping territorial claims that have erupted from time to time into brief confrontations in the South China Sea.

Hostilities between China and the Philippines, however, have worsened since last year, resulting in minor collisions at sea and injuries to a few Filipino crewmen, sparking a war of words.

Washington has no territorial claims in the strategic waterway but has questioned China’s claim to virtually the entire seaway. The United States has repeatedly warned that it’s obligated to defend the Philippines, its oldest treaty ally in Asia, if Filipino forces, ships and aircraft come under an armed attack.

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During the Chinese coast guard’s maneuvers, one of its ships crossed the bow of the Philippine fisheries vessel BRP Datu Sanday at a distance of 100 meters (328 feet), Tarriela said. At least 13 suspected Chinese militia vessels tried to help form a blockade, he said.

Two of the three small sandbars where the Filipino scientists carried out a survey are located between Philippine-occupied Thitu island and Subi, a disputed reef that China transformed into an island base with a military-grade runway, seaports and a number of buildings with communications facilities.

In 2017, Chinese officials accused the Philippine military of attempting to build a structure on one of the sandbars, and deployed Chinese coast guard and suspected militia ships to keep watch on Sandy Cay.