The US has warned China against "aggressive behavior in the South China Sea," saying it would not accept Beijing’s control of the region.
The warning by Admiral Harry Harris, head of the US Pacific Command, came on Wednesday as tensions between two powers continue to rise.
"We will not allow the shared domains to be closed down unilaterally, no matter how many bases are built on artificial features in the South China Sea," Harris said.
"We will cooperate where we can but we will be ready to confront where we must," the admiral told Australian think tank the Lowy Institute in Sydney.
"The US fought its first war following our independence to ensure freedom of navigation, and we did that when we were weak and small," he said, noting “our forces remain ready to fight tonight."
President-elect Donald Trump has questioned America’s commitment to the “one-China” policy in the China-Taiwan row, saying Washington should only side with Beijing on certain conditions.
His direct talk with Taiwanese President Tsai Ing-wen also angered Beijing which is rapidly developing artificial islands in the South China Sea capable of hosting military planes.
Trump told Fox News on Sunday; “I don't know why we have to be bound by a 'one-China policy' unless we make a deal with China having to do with other things, including trade.”
His talk with Tsai was the first one by a US president or president-elect since Washington cut ties with Taipei in 1979 and committed to the “one-China” principle, which recognizes Taiwan as a part of China.
Beijing, in response, urged American officials to avoid sending “any wrong signals to 'Taiwan independence' forces.”
Relations between China and the US have generally been stable, but tensions between them have recently escalated in the wake of Washington’s increased military involvement in Asia as part of President Barack Obama’s “pivot” to the region.
Political observers believe the “pivot” was aimed at countering China’s rise in Asia.