The United States has growing concerns China's maritime claims in the disputed South China Sea are an effort to gain creeping control of oceans in the Asia-Pacific region, a senior US official has said.
In congressional testimony, US Assistant Secretary of State for East Asian and Pacific Affairs Danny Russel said China's vague territorial claims in the South China Sea had "created uncertainty, insecurity and instability" among its neighbours.
While the United States says it does not take sides in disputes, Russel said it had an interest in seeing maritime disputes resolved peacefully.
"There are growing concerns that this pattern of behaviour in the South China Sea reflects incremental effort by China to assert control over the area contained in the so-called 'nine-dash line' despite objections of its neighbours and despite the lack of explanation or apparent basis under international law regarding the scope of the claim itself," Russel told the House of Representatives subcommittee on Asia and the Pacific.
China has put forward historical records - known as the nine-dash line - to depict its claims in the South China Sea. The nine-dash line takes in about 90 per cent of the 3.5-million square kilometre South China Sea on Chinese maps.
Beijing, the Philippines, Vietnam, Taipei, Malaysia and Brunei all have territorial claims across a waterway that provides 10 per cent of the global fisheries catch and carries US$5 trillion in ship-borne trade.
Russel said under international law, maritime claims in the South China Sea had to be based on land features. Beijing should "clarify or adjust its nine-dash line claim to bring it in accordance with the international law of the sea", he added.
To address US concerns, Russel said he and other senior US officials had travelled to the region to raise the issue with China. In prepared remarks for the testimony, he said US Secretary of State John Kerry also would soon visit the region.
Russel said the US was also concerned about the "serious downturn" in China-Japan relations over a tiny set of uninhabited islands in the East China Sea. Both Tokyo and Washington have said they do not recognise China's announcement last year that it has the right to police the skies above the islands.