A US Navy guided-missile destroyer, the USS Decatur, sailed through the South China Sea on Friday in a freedom of navigation operation intended to send a blunt message to China.
White House spokesman Josh Earnest said the point was to let China know that it cannot "unlawfully restrict the navigation rights, freedoms and lawful uses of the sea that the United States and all states are entitled to exercise under international law."
The Pentagon, in a statement, called the USS Decatur's trip "routine" and said it took place "without incident."
The Chinese Defense Ministry said the operation was "illegal" and "provocative" and that two Chinese warships warned the Decatur to leave, according to Reuters.
Tensions in the region have escalated over the last two years as China has claimed land in massive dredging operations in the contested waters, turning sandbars into islands equipped with airfields, ports and lighthouses in some cases. The islands are more than 800 miles from the Chinese mainland.
In July, an international tribunal in the Hague deemed the bulk of China's territorial claims in the South China Sea to have no legal basis under the UN Convention on the Law of the Sea.
The transit of the USS Decatur in the South China Sea was part of a routine operation "in full compliance with international law," according to Pentagon spokesman Cmdr. Gary Ross.
In recent months, Beijing has reacted angrily to US freedom of navigation operations in the region, scrambling fighter jets and boats and denouncing the actions as "threatening Chinese sovereignty."