The Philippines lodged its “strongest protest” against Beijing on Monday and summoned a senior Chinese diplomat over a water cannon assault by the Chinese coast guard that injured Filipino navy crew members and heavily damaged their boat in the disputed South China Sea, officials said.

In response, China warned that relations were at a crossroads and the Philippines should choose a prudent path forward.

Two Chinese coast guard ships hit a Philippine navy-operated supply boat with water cannons Saturday in the latest and most serious confrontation between the rival Asian claimants near the disputed Second Thomas Shoal, which is surrounded by Chinese vessels in a bid to dislodge Philippine forces from there.

The repeated high-seas confrontations since last year have sparked fears of a larger conflict that could put China and the United States on a collision course.. The U.S. has warned repeatedly that it’s obligated to defend the Philippines — its oldest treaty ally in Asia — if Filipino forces, ships or aircraft come under an armed attack, including in the South China Sea.

The United States, the European Union, Japan, Australia and about 16 other countries have expressed support to the Philippines and the rule of law, according to the Department of Foreign Affairs in Manila.