The Philippines' military said late Sunday it held a joint maritime exercise with Japan, the United States and Australia in the South China Sea, leading China to launch a naval and air patrol in response.

The four-nation drill held Sunday within the Philippines' exclusive economic zone demonstrated the countries' "commitment to strengthen regional and international cooperation in support of a free and open Indo-Pacific through interoperability exercises in the maritime domain," the Philippines' armed forces said.

Vessels from Australia, Japan, the Philippines and the United States sail in formation during a joint maritime exercise in the South China Sea on April 7, 2024. (Photo courtesy of the Australian government)(Kyodo)

In a joint statement issued a day before the exercise, the four countries said they intended to "uphold the right to freedom of navigation and overflight and respect for maritime rights under international law" in accordance with the United Nations Convention on the Law of the Sea.

The four countries' forces performed a communication exercise, division tactics and other drills, the Philippines' military said, noting the exercise was joined by Japan Maritime Self-Defense Force destroyer Akebono, a U.S. combat ship Mobile, the Royal Australian Navy frigate Warramunga and Philippine Navy frigate Antonio Luna, among others.

The quadrilateral drill occurred against the backdrop of China's assertiveness in the resource-rich South China Sea.

In a move to counter the drill, the Chinese military said Sunday it conducted a "strategic patrol" under the People's Liberation Army's Southern Theater Command.

"All military activities that disrupt the South China Sea and create hot spots are under control," the military said in a statement.

A 2016 ruling by the Permanent Court of Arbitration invalidated China's claim of sovereignty over almost the entire South China Sea, which was also being claimed in part by the Philippines, Brunei, Malaysia, Vietnam and Taiwan.

Related coverage:

Japan, U.S., Australia, Philippines to hold joint naval drills on April 7

U.S., Chinese forces resume maritime talks, 1st since 2021

Japan, U.S., Australia, Philippines to hold drill in South China Sea