Philippine and U.S. soldiers began their biggest combined military exercise in 15 years on Monday, in a demonstration of Washington's commitment to its long-time ally as it rebalances to Asia in the face of China's expansion in the South China Sea.
The annual "Balikatan" (shoulder-to-shoulder) war games are part of a new U.S. military initiative known as Pacific Pathways, involving a series of drills across the Asia-Pacific as America deploys more troops, ships and aircraft in the region.
"The exercises this week are part of a U.S. rebalance to Asia starting with Balikatan in the Philippines," Major-General Raul del Rosario told Reuters as more than 1,000 US Army troops joined the drills at a jungle army base.
Pacific Pathways, which Washington says is part of a plan to establish a "semi-permanent" U.S. presence in Asia, will comprise 29 exercises across 12 countries in the region over the next five years.
The exercise comes a few days after the Philippines said it was seeking more "substantive" support from the United States on how to counter China's rapid expansion in the South China Sea.
China's rapid reclamation around seven reefs in the Spratly archipelago of the South China Sea has alarmed claimants, including the Philippines and Vietnam, and drawn growing criticism from U.S. government officials and the military.
U.S. President Barack Obama has said Washington is concerned China is using its "sheer size and muscle" to push around smaller nations in the disputed sea, drawing a swift rebuke from Beijing.
"We make no pretense that we are helping the Philippines as it fields a minimum credible defence," U.S. Ambassador Philip Goldberg said at the drills' opening ceremony.
"The U.S. is committed to its alliance ... and the U.S. will defend the important principles of freedom of navigation in the air and the sea."
In Beijing, foreign ministry spokesman Hong Lei said China hoped the U.S. and Philippines "do more that is beneficial to increasing mutual security trust between countries in the region and that is beneficial to regional peace and stability".
More than 11,000 American and Filipino troops are taking part in the 10-day drill on the islands of Luzon, Palawan and Panay. The war games will see U.S. fighters rehearse bombing runs and troops involved in live fire drills.
Dozens of leftwing activists protested outside the U.S. embassy in Manila, saying the Americans were using China as a bogeyman to gain a forward base in the Philippines.