MANILA, Philippines (AP) — The United States renewed a warning Tuesday that it’s obligated to defend its close treaty ally a day after Filipino navy personnel were injured and their supply boats damaged in one of the most serious confrontations between the Philippines and China in a disputed shoal in the South China Sea, officials said.

China and the Philippines blamed each other for instigating Monday’s hostilities in the Second Thomas Shoal, which has been occupied by a small Filipino navy contingent aboard a grounded warship that’s been closely watched by Chinese coast guard, navy and suspected militia ships in a yearslong territorial standoff. There is fear the disputes, long regarded as an Asian flashpoint, could escalate and pit the United States and China in a larger conflict.

U.S. Deputy Secretary of State Kurt Campbell discussed China’s actions with Philippine counterpart, Maria Theresa Lazaro, in a telephone call. Both agreed that China’s “dangerous actions threatened regional peace and stability,” State Department spokesperson Matthew Miller said.

Campbell reaffirmed that the 1951 Mutual Defense Treaty, which obligates Washington and Manila to help defend the other in major conflicts, “extends to armed attacks on Philippine armed forces, public vessels, or aircraft – including those of its coast guard – anywhere in the South China Sea,” according to Miller.

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A Philippine government task force overseeing the territorial disputes condemned what it said were “dangerous maneuvers, including ramming and towing,” which disrupted a routine effort to transport food, water and other supplies to the Filipinos manning the territorial outpost aboard the BRP Sierra Madre at the shoal.

“Despite the illegal, aggressive, and reckless actions by the Chinese maritime forces, our personnel showed restraint and professionalism, refrained from escalating the tension, and carried on with their mission,” the Philippine task force said without elaborating. “Their actions put at risk the lives of our personnel and damaged our boats in blatant violation of international law.”

The Chinese coast guard said the Philippines “is entirely responsible for this.” It said a Philippine vessel “ignored China’s repeated solemn warnings … and dangerously approached a Chinese vessel in normal navigation in an unprofessional manner, resulting in a collision.”

Two speedboats — attempting to deliver construction materials and other supplies to a military vessel stationed at the shoal — accompanied the supply ship, according to China’s Foreign Ministry, which described its coast guard’s maneuver as “professional, restrained, reasonable and lawful.”

Philippine Defense Secretary Gilberto Teodoro Jr. said Monday night that his country’s armed forces would resist “China’s dangerous and reckless behavior,” which “contravenes their statements of good faith and decency.”

“We will exert our utmost in order to fulfill our sworn mandate to protect our territorial integrity, sovereignty, and sovereign rights,” Teodoro said. “It should now be clear to the international community that China’s actions are the true obstacles to peace and stability in the South China Sea.”

Several incidents have happened in recent months near the shoal which lies less than 200 nautical miles (370 kilometers) from the nearest Philippines coast and where it maintains the Sierra Madre, which had become encrusted with rust since it was deliberately grounded in 1999 but remains an actively commissioned military vessel, meaning an attack on it could be considered by the Philippines as an act of war.

China has increasingly become assertive in pressing its claim to virtually the entire South China Sea, which has led to a rising number of direct conflicts with other countries in the region, most notably the Philippines and Vietnam.

A new law by China, which took effect Saturday, authorizes its coast guard to seize foreign ships “that illegally enter China’s territorial waters” and to detain foreign crews for up to 60 days. The law renewed a reference to 2021 legislation that says China’s coast guard can fire upon foreign ships if necessary.

At least three coastal governments with claims to the waters — the Philippines, Vietnam and Taiwan — have said they would not recognize the law. Malaysia and Brunei are also involved in the long-seething territorial disputes, which are regarded as a delicate fault line in the longstanding U.S.-China rivalry in the region.

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Associated Press journalists Aaron Favila and Joeal Calupitan in Manila contributed to this report.