US and Philippine forces have launched their largest joint combat exercises in years on the Philippines' northern coast near the disputed South China Sea.

In Mondays mock battle scenario, American and Filipino forces took positions at the airfield, ringed by low-lying hills, as three Army CH-47 Chinook helicopters landed to deliver combat supplies. The troops fired missiles and artillery.

The annual exercises by the longtime treaty allies will run until May 10. The drills involve more than 16,000 of their military personnel, along with more than 250 French and Australian forces.

This years exercises are meant to deter possible aggression. They come against the backdrop of increased confrontations between Chinese and Filipino vessels around shoals in the South China Sea, as well as stepped-up Chinese air and naval activity around nearby Taiwan.

Washington and Manila say the drills are not directed at any country and are crucial for improving the response to emergencies in the Philippines, one of the worlds most disaster-prone countries.

However, this years drills focus on territorial defense and are being staged mainly in two of the most sensitive fault lines in the regional rivalry between China and the United States: the disputed South China Sea and the Bashi Channel.

The critical waterway between Taiwan and the Philippines, an important trade conduit laden with international undersea cables, has been closely watched and guarded by Chinese and American forces.
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