The United States renewed a warning Monday that it would defend the Philippines in case of an armed attack under a 1951 treaty, after Chinese ships blocked and collided with two Filipino vessels off a contested shoal in the South China Sea.

Philippine diplomats summoned a Chinese Embassy official in Manila on Monday for a strongly worded protest following Sunday’s collisions off Second Thomas Shoal. No injuries were reported but the encounters damaged a Philippine coast guard ship and a wooden-hulled supply boat operated by navy personnel, officials said.

President Ferdinand Marcos Jr. called an emergency meeting with the defense secretary and other top military and security officials to discuss the latest hostilities in the disputed waters. The Philippines and other neighbors of China have resisted Beijing’s sweeping territorial claims over virtually the entire South China Sea, and some, like Manila, have sought U.S. military support as incidents multiply.