The United States and the Philippines opened one of their largest-ever joint military exercises on Monday against the backdrop of an increasingly assertive China in the disputed South China Sea.

The Philippine-led annual exercise, called Balikatan, will involve 5,100 American military personnel and 3,800 members of the Armed Forces of the Philippines in a range of drills including maritime security, amphibious operations, live-fire training, aviation operations, counterterrorism and disaster relief.