"The US defence secretary has accused China of "destabilising" the South China Sea, saying its action threatened the region's long-term progress.
Chuck Hagel said the US would "not look the other way" when nations ignored international rules.
Mr Hagel was speaking at a three-day summit - the Shangri-La Dialogue in Singapore - that involves the US and South-East Asian countries.
He also urged Thailand's coup leaders to restore democratic rule soon.
The forum comes amid growing tensions between China, Vietnam and the Philippines, with Japan-China ties also strained over disputed islands in the East China Sea."