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

In a statement on Thursday, the military said without the approval of the government, the guided-missile destroyer Milius illegally intruded into China’s territorial waters.

The move, the statement said, undermined 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.

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

The US 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.