A Chinese coastguard ship used a water cannon last month to drive Filipino fishermen out of disputed waters in the South China Sea, illustrating aggressive enforcement of new Chinese rules, the head of the Philippine military said on Monday.

China has since the beginning of the year required foreign fishing boats to get approval before entering waters that China claims as its own.

“The Chinese coastguard tried to drive away fishermen to the extent of using water cannon,” Armed Forces Chief of Staff General Emmanuel Bautista told foreign correspondents, referring to a January 27 incident near the Scarborough Shoal.

China claims about 90 percent of the South China Sea’s 3.5 million sq km (1.35 million sq mile) waters. The sea provides 10 percent of the global fish catch, carries $5 trillion in ship-borne trade a year and is believed to be rich in energy.

Taiwan, Malaysia, the Philippines, Brunei and Vietnam also claim parts of the sea.

Bautista declined to give more details about the confrontation in the area, about 130 nautical miles west of the main Philippine island of Luzon, saying the military still had to talk to the fishermen.

He said the Philippine military would try to avoid confrontation with China but would react if China used violence against Philippine fishermen.

Chinese Foreign Ministry spokeswoman Hua Chunying said she was not aware of details of the situation, and repeated that China had sovereignty over the South China Sea and its islands.

“The relevant Chinese maritime forces carry out normal official patrols in that area,” she told a daily news briefing.

A senior Philippine navy official said it was the first time China used water cannon in the area.

“Our fishermen are used to playing a dangerous cat-and-mouse game but China has become very aggressive,” said the navy official who declined to be identified because he is not authorized to speak to the media.

The Philippines has taken its dispute with China to arbitration under the U.N. Convention on the Law of the Sea but China is refusing to participate in the case.

China has rejected challenges to its sovereignty claims and accused the Philippines of illegally occupying Chinese islands in the seas and of provoking tension.

This month, the commander of the U.S. Navy said the United States would come to the aid of the Philippines in the event of conflict with China over disputed waters.

The U.S. ambassador to the Philippines, Philip Goldberg, who was attending the same forum as Bautista, urged the Association of South East Asian Nations and China to accelerate negotiations on a code of conduct for the sea to avoid accidents and miscalculations.

“We believe that the agreement on the code of conduct is long overdue,” Goldberg said, adding that the United States supported Philippine efforts to bring the dispute to international arbitration.

2014 Thomson Reuters Foundation