China’s military closely monitored and “drove away” USS Halsey that entered the territorial waters of Paracel Islands in the South China Sea on May 10, the Southern Theater Command of the People’s Liberation Army said in a statement on Friday.

The U.S. move “seriously infringed on China’s sovereignty and security,” the military said.

“It is yet another iron proof of its navigation hegemony and militarization of the South China Sea,” it said, adding its troops would stay on high alert and safeguard national security.

The U.S. Navy said in a statement the destroyer asserted navigational rights and freedoms in the South China Sea near the Paracel Islands “consistent with international law.”

The USS Halsey exited the area after its operation and continued on in the South China Sea, the statement said.

The latest dispute between China and the U.S. came amid heightened tensions in the strategic South China Sea, with U.S. ally the Philippines embroiled in an bitter diplomatic row with Beijing over disputed waters in the region. China claims large swaths of the South China Sea, including parts claimed by the Philippines, Vietnam, Indonesia, Malaysia and Brunei. The Permanent Court of Arbitration in 2016 ruled that Beijing’s claims had no basis under international law.