The Chinese People's Liberation Army (PLA) said on Tuesday it had warned the USS Chancellorsville guided-missile cruiser off China's territorial waters as the warship sailed near the Nansha Islands.

The USS Chancellorsville's "illegal intrusion" was done without approval by the Chinese government, PLA Southern Theater Command spokesperson Tian Junli said, adding that the PLA has been tracking and monitoring the cruiser with both air and naval deployments.

The actions of the U.S. military have seriously violated China's sovereignty and security and served as further proof that it is militarizing the South China Sea, fully demonstrating that the U.S. is "a security risk maker" in the region, Tian said.

China's sovereignty over the Nansha Islands and their adjacent waters is irrefutable, Tian said, adding that his command will remain on high alert and will firmly safeguard national sovereignty and security, as well as peace and stability in the region.

(Cover: A guided-missile cruiser the USS Chancellorsville can be seen on the sea, June 18, 2016. /CFP)