The United States has reaffirmed its commitment to the Mutual Defense Treaty with the Philippines following the “unsafe and irresponsible” actions of a Chinese military helicopter against a Philippine aircraft over Bajo de Masinloc.

In a statement on Wednesday (US time), US State Department Spokesperson Tammy Bruce expressed support for the Philippines in condemning the Chinese People’s Liberation Army Navy (PLAN) for interfering with the Philippines’ operations in the area.

“Reckless Chinese actions such as these are a threat to navigation and overflight in the South China Sea, and we will continue to support our allies and partners to ensure a free and open Indo-Pacific,” Bruce said.

“We call on China to refrain from coercive actions and settle its disputes peacefully in accordance with international law,” she added.

She also emphasized that the defense agreement between Manila and Washington may be invoked in response to armed attacks on Philippine vessels anywhere in the South China Sea.

“The 1951 United States-Philippines Mutual Defense Treaty extends to armed attacks on Philippine armed forces, public vessels, or aircraft — including those of its Coast Guard — anywhere in the South China Sea,” she stressed.

Signed in 1951, the MDT’s Article IV states that each party — the U.S. and the Philippines — “recognizes that an armed attack in the Pacific area on either of the parties would be dangerous to its own peace and safety and declares that it would act to meet the common dangers in accordance with its constitutional processes.”

On Tuesday, the Philippine Coast Guard (PCG) reported that a PLAN helicopter with tail number 68 performed “dangerous flight maneuvers” against the Bureau of Fisheries and Aquatic Resources (BFAR) aircraft flying over Bajo de Masinloc, also known as Scarborough Shoal.

According to PCG spokesperson for the West Philippine Sea, Commodore Jay Tarriela, the “reckless action” of the Chinese military helicopter “posed a serious risk” to the safety of the pilots and passengers conducting maritime domain awareness flights within the country’s territorial airspace.

Tarriela stressed the PLA Navy's “clear violation and blatant disregard” for the International Civil Aviation Organization’s international aviation regulations.

‘Illegal trespassing’

For its part, China justified its actions, stressing that the Philippine aircraft “illegally trespassed” into its airspace without permission.

Citing Senior Colonel Tian Junli, PLA Southern Theater Command spokesperson, Chinese state-owned media Global Times said Tian also accused the Philippines of spreading false narratives.

“The PLA Southern Theater Command organized naval and air forces and tracked, monitored, warned, and expelled it in accordance with laws and regulations,” he said.

China claims the vast South China Sea, including the West Philippine Sea, which is within the Philippines' 200-nautical-mile exclusive economic zone.

China’s historic “nine-dash line” claim, however, was rejected by the Permanent Court of Arbitration in 2016 after it ruled in favor of Manila’s sovereign rights in the area. China has rejected the award, calling it “illegal, null, and void.”