A Chinese Coast Guard ship attacked a Philippine government vessel near the Scarborough Shoal on Friday, using a water cannon to drive the Philippine ship out of waters claimed by China.

The Scarborough Shoal is a small, rocky land mass about 120 nautical miles west of the Philippine island of Luzon. The entire formation covers less than 60 square miles.

Both Beijing and Manila claim to own the shoal and its surrounding waters, referring to the feature as Huangyan Island and Bajo de Masinloc, respectively. The English term for the feature derives from the name of a British merchant ship that ran aground on it in 1748.

The Philippine claim is based on historical maps and documents that trace the history of the Scarborough Shoal as a Spanish colonial possession, and then a Japanese conquest during World War II. One of the key pieces of evidence is a map drawn in 1734 that unambiguously depicts the shoal as part of the Philippine island chain.

When the U.S. held sovereignty over the Philippines, the Scarborough Shoal was part of its administrative territory, so when the Philippines became independent in 1946, the new government felt the Scarborough Shoal was naturally part of the package. The shoal is located within the Exclusive Economic Zone (EEZ) of the Philippines.

The Chinese disagreed, making claims based on even older 14th-century maps that the Scarborough Shoal, and indeed virtually all of the South China Sea, are Chinese territory. An international tribunal rejected China’s expansive claims in 2016, but Beijing simply ignored the court ruling and began taking over much of the region by force.

The Philippines is primarily interested in the Scarborough Shoal as an excellent fishing ground, and as a place where fishermen can take shelter from bad weather. Chinese fishermen also covet those fishing grounds, and there are untapped oil and gas reserves nearby.

In April 2012, a landmark conflict occurred around the shoal when the Philippines dispatched a naval frigate to chase Chinese fishermen away, and China sent its own ships to push back, The confrontation led to the international court case that China would ultimately lose, and also marked the beginning of China’s effort to use various forms of intimidation to take effective control of the feature.

On Thursday, China accused the Philippines of “illegally” operating near two other nearby features, the Half Moon and Royal Captain Shoals. The following day, a Chinese coast guard vessel used a water cannon against a Philippine government ship.

“The Philippine government vessels, under the pretext of so-called fishery protection, have illegally infringed upon China’s rights and provocatively undermined stability in the South China Sea,” Chinese coast guard spokesman Liu Dejun claimed on Friday.

“The Philippine side’s actions constitute a serious violation of China’s sovereignty and international law,” said Liu.

The Philippine Coast Guard (PCG) responded on Friday, accusing China of using aggressive maneuvers to interfere with a resupply mission for Filipino fishermen conducted by ships from the Bureau of Fisheries and Aquatic Resources (BFAR).

According to the Philippine statement, one of the four BFAR ships involved in the mission was struck by a Chinese water cannon, but “adeptly maneuvered” around the Chinese ship to “avoid significant damage.” Another Philippine ship was targeted, but the Chinese attacker “missed its mark.”

“Despite the unprofessional and illegal actions of the Chinese Coast Guard, which endangered Filipino crew members and fishermen, BFAR vessels remained resolute in their mission to protect local fishing boats,” the PCG said.

Stars and Stripes reported on Tuesday that China has “expanded its patrols east of the shoal” over the past ten months, so it can intercept more Philippine ships and provoke confrontations like the water cannon incident. There have also been some dangerous encounters between Chinese and Filipino aircraft, whereas previous confrontations were mostly between surface vessels.

“The confluence of increasingly frequent aerial encounters and maritime interactions near Scarborough Shoal inevitably increases the chance of accidental escalation between Chinese and Philippine forces, which could ultimately trigger U.S. treaty obligations and risk spiraling into a wider conflict,” warned a report from the Asia Maritime Transparency Initiative cited by Stars and Stripes.