The US has accused China of conducting missile launches in the South China Sea, describing Beijing's actions as "meant to intimidate".
US media first reported the launches citing unnamed Pentagon officials.
Beijing had announced military drills but did not confirm the allegations that it launched missiles in the disputed waters.
Taiwan, the Philippines, Brunei, Malaysia and Vietnam all make claims to parts of the sea.
China however claims a huge area known as the "nine-dash line" and has been building military installations on artificial islands there.
Ahead of the exercise Beijing warned other ships not to enter a designated area between the Spratly and Paracel Islands for five days.
Washington "was aware of the Chinese missile launch from the man-made structures in the South China Sea near the Spratly Islands," Pentagon spokesman Lieutenant Colonel Dave Eastburn said on Tuesday.
He added that China's behaviour was "contrary to its claim to want to bring peace to the region and obviously actions like this are coercive acts meant to intimidate other claimants" to the South China Sea.
The sea, home to vital shipping lanes, has in recent years become a flashpoint for tensions between China and other regional nations which have overlapping claims over islands and reefs.
China routinely accuses the US Navy of provocation and interference in regional matters.
The US has long been critical of what it says is China's militarisation of the region and routinely angers Beijing with "freedom of navigation" missions.