Using unusually strong language, US Defense Secretary Chuck Hagel took aim at Beijing's handling of territorial disputes with its Asian neighbors.
"In recent months, China has undertaken destabilizing, unilateral actions asserting its claims in the South China Sea," Hagel said.
He warned Beijing that the United States was committed to its geopolitical rebalance to the Asia-Pacific region and "will not look the other way when fundamental principles of the international order are being challenged".
Hagel said the United States took no position on the merits of rival territorial claims in the region, but added: "We firmly oppose any nation's use of intimidation, coercion, or the threat of force to assert these claims."
His speech at Singapore's Shangri-La Dialogue, Asia biggest security forum, provoked an angry reaction from the deputy chief of staff of the Chinese Army, Lieutenant-General Wang Guanzhong.
"I felt that Secretary Hagel's speech is full of hegemonism, threat and intimidation," he told reporters just after the speech.
Wang said the speech was aimed at causing trouble in the Asia-Pacific.