MANILA, Philippines (AP) — The United States renewed a warning that it would defend its treaty ally if Filipino forces come under attack in the disputed South China Sea, after a Chinese coast guard ship allegedly hit a Philippine patrol vessel with military-grade laser that briefly blinded some of its crew.

The Department of Foreign Affairs in Manila sent a strongly worded diplomatic protest to the Chinese Embassy Tuesday that “condemned the shadowing, harassment, dangerous maneuvers, directing of military-grade laser, and illegal radio challenges” by the Chinese ship.

The incident took place Feb. 6. when the Chinese coast guard ship beamed high-grade lasers to block the Philippine patrol vessel BRP Malapascua from approaching Second Thomas Shoal on a resupply mission to Filipino forces there, according to Philippine officials.

China claims the South China Sea virtually in its entirety, putting it on a collision course with other claimants. Chinese naval forces have been accused of using military-grade lasers previously against Australian military aircraft on patrol in the South China Sea and other spots in the Pacific.

Despite friendly overtures to Beijing by former Philippine President Rodrigo Duterte and his successor, Ferdinand Marcos Jr., who met Chinese leader Xi Jinping in January in Beijing, tensions have persisted, drawing in closer military alliance between the Philippines and the U.S.

Chinese Foreign Ministry spokesperson Wang Wenbin said Monday that a Philippine coast guard vessel trespassed into Chinese waters without permission. Chinese coast guard vessels responded “professionally and with restraint at the site in accordance with China’s law and international law,” he said, without elaborating or mentioning the use of laser.

U.S. State Department spokesperson Ned Price said China’s “dangerous operational behavior directly threatens regional peace and stability, infringes upon freedom of navigation in the South China Sea as guaranteed under international law and undermines the rules-based international order.”

“The United States stands with our Philippine allies,” Price said in a statement.

He said that an armed attack on Philippine armed forces, public vessels, or aircraft, including those of the coast guard in the South China Sea, would invoke U.S. mutual defense commitments under a 1951 treaty. The treaty obligates the allies to help defend one another in case of an external attack.

Aside from China and the Philippines, Vietnam, Malaysia, Taiwan and Brunei also have overlapping claims in the resource-rich and busy waterway, where a bulk of the world’s commerce and oil transits.

Washington lays no claims to the disputed sea but has deployed forces to patrol the waters to promote freedom of navigation and overflight — moves that have angered Beijing, which has warned Washington to stop meddling in what it says is a purely Asian dispute.

The contested waters have become a volatile front in the broader rivalry between the U.S. and China in Asia and beyond.

Price said the Chinese coast guard’s “provocative and unsafe” conduct interfered with the Philippines’ “lawful operations” in and around Second Thomas Shoal.

In July, U.S. Secretary of State Antony Blinken called on China to comply with a 2016 arbitration ruling that invalidated Beijing’s vast territorial claims in the South China Sea and warned that Washington was obligated to defend the Philippines under the Mutual Defense Treaty.

On Monday, Price reiterated that the “legally binding decision” underscored that China “has no lawful maritime claims to the Second Thomas Shoal.” China has long rejected the ruling and continues to defy it.

The Philippines filed nearly 200 diplomatic protests against China’s aggressive actions in the disputed waters in 2022 alone.

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Associated Press writer Matthew Lee in Washington, D.C., contributed to this report.