With tensions already high over Beijing's imposition of an air zone above islands administered by Japan in the East China Sea, fears are growing of a fresh showdown in a separate row in the South China Sea where the Philippines is especially concerned.
Addressing the rifts, the top US diplomat for the region challenged Beijing's so-called "nine-dash line" that outlines its territorial claims over much of the South China Sea.
Danny Russel, the US assistant secretary of state for East Asian and Pacific affairs, yesterday said that maritime claims under international law needed to be based on land features.
"China could highlight its respect for international law by clarifying or adjusting its claim to bring it into accordance with international law of the sea," he said.
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Russel supported the Philippines' right to take its case to a United Nations tribunal -- a move last year that was denounced by China -- as part of efforts to find a "peaceful, non-coercive" solution.
"China's lack of clarity with regard to its South China Sea claims has created uncertainty in the region and limits the prospect for achieving mutually agreeable resolution or equitable joint development arrangements," Russel said.
But the United States, while boosting military cooperation with allies Japan and the Philippines, has generally stressed that it takes no stance on sovereignty in Asia's myriad disputes -- a position that Russel reiterated.