US Secretary of State John Kerry said China would be committing a provocative and destabilising act if it establishes an air defence zone in the South China Sea.
Kerry said doing so would raise tensions between China and other Asian countries.
He said such an act also would call into question China’s commitment to resolving disputes over islands and maritime claims diplomatically.
Kerry said the US doesn’t take sides on competing claims.
He said no country should move unilaterally to militarise the resource-rich region.
Kerry spoke to reporters while visiting Mongolia. He travels on to China later today for annual US-China strategic and economic talks.