The United States on Wednesday warned China against what the Philippines and Taiwan see as increasingly aggressive moves, reminding Beijing of Washington's obligations to its partners.

"An armed attack against the Philippines' armed forces, public vessels or aircraft in the Pacific, including in the South China Sea, will trigger our obligations under the US-Philippines Mutual Defense Treaty," State Department spokesman Ned Price told reporters.

"We share the concerns of our Philippine allies regarding the continued reported massing of PRC maritime militia near the Whitsun Reef," Price said, referring to the People's Republic of China.

More than 200 Chinese boats were first spotted on March 7 at Whitsun Reef, around 320 kilometers (200 miles) west of Palawan Island in the contested South China Sea, although many have since scattered across the Spratly Islands.

China, which claims almost the entirety of the resource-rich sea, has refused weeks of appeals by the Philippines to withdraw the vessels, which Manila says unlawfully entered its exclusive economic zone.

Tensions have also risen with Taiwan, which Beijing claims as part of China, with the self-governing democracy on Wednesday reporting that 15 more of the mainland's planes crossed into the island's air defense zone.

Price voiced "concern" about the Chinese moves, saying: "The United States maintains the capacity to resist any resort to force or other forms of coercion that would jeopardize the security or the social or economic system of the people on Taiwan."

He was using language from the Taiwan Relations Act, under which the United States is obliged to provide the island with the means to defend itself against Beijing.

President Joe Biden has vowed a robust defense of allies and, in a rare point of continuity with his predecessor Donald Trump, has supported strong pushback against Chinese assertiveness.

U.S. Navy, Malaysia's air force hold South China Sea bilateral exercises
 Washington DC (UPI) Apr 7, 2021 –

The USS Theodore Roosevelt Carrier Strike Group completed exercises in the South China Sea with Malaysia's air force, the U.S. Navy said on Wednesday.

The aircraft carrier and Carrier Wing 11, escorted by the guided missile cruiser USS Bunker Hill and destroyers USS Russell and USS John Finn, conducted the bilateral exercise with the Royal Malaysian Air Force on Tuesday and Wednesday.

"Su-30MKM [Russian-made fighter planes] and F/A-18D aircraft represent the RMAF, while USN is represented by F/A-18 E/F and EA-18G aircraft from the USS Theodore Roosevelt Carrier Strike Group," a statement on the website of the RMAF, known as the Tudm Rasmi, said on Wednesday.

The strike group and RMAF planes conducted Dissimilar Air Combat Training exercises, in which superior planes maneuver against less nimble planes, joint-air operations and unit integration, the U.S. Navy said.

"We are thankful for the opportunity to train alongside the Royal Malaysian Air Force," Rear Adm. Doug Verissimo, commander of Carrier Strike Group Nine, said in the Navy release.

"While we would have loved to meet face to face, I am excited that we can meet in the air to help deepen security cooperation between our two nations," Verissimo said.

The United States' military alliance with Australia and New Zealand makes Malaysia, a member of the Five Power Defense Arrangements treaty with Australia, New Zealand, Singapore and Britain, a U.S. military ally. Malaysia has also been involved in territorial disputes with China.

The bilateral exercises in the South China Sea concluded as the destroyer USS John S. McCain sailed through the nearby Taiwan Strait, drawing the criticism of China's military.