The US slammed China for its "escalation" in the key global shipping route where Beijing is accused of deploying warships, arming outposts and ramming fishing vessels. Most recently, Vietnam voiced concerns on China's movements near Spratly Islands.
China and the US have repeatedly traded barbs in the past over what Washington says is Beijing's militarisation of the South China Sea. China blames the US for sending warships and military planes, saying they ratchet up tension in the region.