American planes took off; China raised planes

The response came immediately from China, which announced that it had carried out air and naval combat patrols in the same region.

In a joint statement by the military officials of the four countries, it is stated that "the action will be carried out in a manner that is by international law and with respect for the safety of navigation and the rights and interests of other countries."

A Philippine military official said navy ships and fighter jets will conduct anti-submarine drills and combined maneuvers.

China has long claimed much of the South China Sea, a major global trade sea route, and has said it will defend its territorial interests at all costs.

Its claims overlap with those of smaller states, such as the Philippines and Vietnam, as they impede access to fishing grounds and oil and gas exploration in their internationally recognized economic zones.

Hostilities in the disputed waters have particularly escalated between Chinese and Philippine coast guards and naval forces in the past year, raising fears that the clashes could escalate into a larger armed conflict involving the United States, a longtime ally of the Philippines.