SUBIC, Philippines (AP) — More than 2,000 U.S. and Philippine military personnel, along with a small contingent of Japanese forces, have begun an annual combat exercise aimed at responding rapidly to crises and natural disasters, underscoring their commitment to keep the region "free and open."

The 10-day drills, which include amphibious assault and live-fire exercises, opened Wednesday at Subic Freeport northwest of Manila. They will also include humanitarian work in six northern Philippine provinces.

China has often branded military exercises involving the U.S. and its allies, especially in or near the disputed South China Sea, as a threat to its security interests. U.S. and Philippine officials say the exercises aim to address terrorism and humanitarian concerns.