PALAWAN, Philippines — U.S., Filipino and Australian troops dug into beach dunes and unleashed a barrage of firepower — including high-powered rockets — during Balikatan training aimed this week at repelling an amphibious assault.

China and the Philippines have each unfurled their national flags on tiny sandbars in the South China Sea, staking competing sovereignty claims in strategic waters seen as a potential flashpoint for global conflict.

The standoff over Sandy Cay, which lies close to military outposts built by both Beijing and Manila, was the latest between the two nations.