China sent fighter jets out in response to what it considers an illegal US naval incursion into a disputed reef.
Reuters reports that the USS William P. Lawrence closed to within 12 nautical miles (22 km) of the Fiery Cross Reef as part of a "freedom of navigation operation" to "challenge [China's] excessive maritime claims."
"These excessive maritime claims are inconsistent with international law as reflected in the Law of the Sea Convention in that they purport to restrict the navigation rights that the United States and all states are entitled to exercise," said a US Defense Department spokesperson.
China has been building artificial islands in the South China Sea and declaring them to be its sovereign territory.