China’s military said on Thursday it had monitored and driven away a US destroyer that illegally entered waters around the Paracel Islands in the South China Sea.

In a statement, the military said that the guided-missile destroyer USS Milius intruded into China’s territorial waters, undermining peace and stability in the busy waterway.

“The theatre forces will maintain a high state of alert at all times and take all necessary measures to resolutely safeguard national sovereignty and security and peace and stability in the South China Sea,” said Tian Junli, a spokesman for China’s Southern Theatre Command.

The US Navy on Thursday disputed the Chinese military statement, saying the destroyer is conducting “routine operations” in the South China Sea and was not expelled.

“The United States will continue to fly, sail, and operate wherever international law allows,” a statement from the US Navy 7th Fleet said.

Tension between the United States and China has been growing in the area.

The United States has been shoring up alliances in the Asia-Pacific seeking to counter China’s assertiveness in the South China Sea and the Taiwan Strait, as Beijing seeks to advance its territorial claims.