U.S. and Filipino troops fired missiles and artillery at an imaginary "invasion" force during war games on the Philippines' northern coast Monday, days after their governments objected to China's "dangerous" actions in regional waters.

Thousands of troops are conducting land, sea and air maneuvers against a backdrop of increased confrontations between Chinese and Filipino vessels around shoals in the South China Sea claimed by Manila, as well as stepped-up Chinese air and naval activity around nearby self-ruled Taiwan.

U.S. troops massed at a strip of sand dunes on Luzon island's northwest coast — around 400 kilometers (249 miles) south of Taiwan — let loose more than 50 live 155mm howitzer rounds at floating targets about 5 km off the coast.