Some countries appear to view freedom of the seas as "up for grabs" in the South China Sea, imposing superfluous warnings and restrictions that threaten stability, a U.S. Navy commander said Tuesday in comments apparently aimed at China.

Adm. Scott Swift, commander of the U.S. Pacific Fleet, said in a strongly worded address in Australia the United States remained "as committed as ever" to protect freedom of navigation through the region.

"It's my sense that some nations view freedom of the seas as up for grabs, as something that can be taken down and redefined by domestic law or by reinterpreting international law," Swift told a maritime conference in Sydney.