A Chinese military spokesman has said the People's Liberation Army will remain "on high alert and take all necessary measures" to protect what it claims is its "national sovereignty" after the U.S. Navy sent two warships near two Chinese-held man-made islands in the disputed South China Sea.

Senior Col. Li Huamin, a spokesperson for the PLA's Southern Theater Command, said the military had sent warships and aircraft to warn off the guided-missile destroyers USS Preble and USS Chung Hoon after the two vessels conducted what the U.S. calls "freedom of navigation operations" (FONOP) Monday near two islets in the South China Sea's Spratly island chain.

China's Foreign Ministry also confirmed the operation, saying that the sailings had "violated China's sovereignty and undermined peace, security and healthy order in the relevant sea areas."