File photo shows the Jinqing Island of Yongle Islands, located in the Xisha Islands, in south China's Hainan Province. (Xinhua/Guo Cheng)

The Chinese military on Thursday monitored a U.S. warship that entered Chinese territorial waters without permission and warned it to leave, Senior Colonel Li Huamin, spokesperson of the Southern Theater Command of the People's Liberation Army (PLA), said in a statement.

The warning came after the USS Mustin entered territorial waters off the Xisha Islands in the South China Sea on Thursday without China's permission. Such an act is hegemonic behavior which violates the international law, Li said.

The command will continue to watch closely Chinese waters and air to prevent any incident that may harm China's national security and to safeguard national sovereignty, Li added.