The United States, Canada, Japan, and the Philippines conducted a two-day joint maritime exercise in Manila's exclusive economic zone in the South China Sea, the U.S. Pacific Fleet said on its website on Monday.

The maritime cooperative activity was aimed at "upholding freedom of navigation and overflight, reaffirming the four nations' commitment to bolstering regional security and stability," the U.S. Pacific Fleet said.

It involved four warships and a series of maritime manoeuvres to test and validate the interoperability of our armed forces' doctrines, tactics, techniques, and procedures, it added.

In April, the Philippines conducted joint maritime activity with Japan, Australia, and the United States.

The Philippines has turned to countries supportive of its claims in the South China Sea to counter what Manila regards as the increasing aggressiveness of China, which claims almost the entire strategic waterway.

Brunei, Malaysia, Taiwan, and Vietnam have competing claims of sovereignty in portions of the South China Sea, a passage through which $3 trillion in goods move every year.