The United States has deployed an aircraft carrier and several escorts to the South China Sea in an apparent show of force to China.
The John C. Stennis, along with two destroyers and two cruisers, reportedly arrived in the disputed waters earlier this week. A U.S. flagship is also in the region.
China claims almost the entire South China Sea. The United States has accused Beijing of militarizing the region as it tries to contest territorial claims by other nations.
After China deployed surface-to-air missiles on the Paracel Islands last month, the head of the U.S. Pacific Command, Admiral Harry Harris, told Congress that China is clearly militarizing the sea.
"You'd have to believe in a flat Earth to believe otherwise," Harris testified.
China denies the accusation and says it is the U.S. that is causing the tension.
"If you take a look at the matter closely, it's the U.S. sending the most advanced aircraft and military vessels to the South China Sea," said a spokeswoman for Beijing's Foreign Ministry, who warned that such a buildup could lead to a "miscalculation."
Pacific Fleet officials say the United States has routinely patrolled the Pacific, including the South China Sea, for decades and has no intention of easing up.
U.S. Defense Secretary Ash Carter told a group of U.S. troops Friday that China's rise as a prosperous nation "is fine. China's aggressive behavior is not, and we and lots of our partners... look to us to apply a counterweight to check anything excessive."
Six Pacific nations — including Vietnam and the Philippines — have territorial claims in the South China Sea, and accuse China of using its military might to intimidate them into backing down.
China also has been building artificial islands in the sea to try to strengthen its claims.