"There's no legal basis for the PRC's maritime claims in the South China Sea and the dangerous ways in which it attempts to enforce those claims put Filipino lives and livelihood at risk," State Department spokesman Matthew Miller told reporters, using the official name for the People's Republic of China.

"It is up to the Philippines to decide how they operate their vessels in areas where it enjoys the freedom of navigation in the high seas under international law," Miller said.

"We continue to support our Philippine allies," he said.

Beijing claims most of the South China Sea despite an international tribunal ruling that its assertions have no merit, and it has acted aggressively against Philippine government vessels at Sabina Shoal and other disputed features in the strategic waterway.

Recent months have seen Chinese sailors ram, block, water-cannon and even board Philippine vessels, causing damage and injuries.

China's coast guard said Sunday it had "indisputable sovereignty" over Sabina Shoal, which it calls Xianbin Jiao, after the Philippines withdrew its flagship BRP Teresa Magbanua.

The Philippines insisted on Monday that it was not a defeat and that it was repositioning the vessel.