About 8,000 U.S. and Filipino troops began annual military exercises on Monday against a backdrop of tension over China's greater assertiveness in the South China Sea though a Philippine commander played that down as the reason for the drills.

Over the next two weeks, the allies will test their command-and-control, communications, logistics and mobility procedures to address humanitarian and maritime security, Philippine defense officials said.

Their troops will also simulate retaking an oil-and-gas platform and practice an amphibious landing on a Philippine beach.

"The Balikatan exercise is designed not to address a particular concern but the whole lump in the spectrum of warfare," Vice Admiral Alexander Lopez, the Philippine military's exercise director, told a news conference.

"China is not part of the idea."