China and the United States exchanged accusations at the weekend over the disputed South China Sea, after China’s military said it had driven away a U.S. warship that the U.S. Navy said was on a routine freedom of navigation operation.

According to a post on the official WeChat social media account of the Chinese People’s Liberation Army Southern Theatre Command on Saturday, the Chinese military deployed its naval and air forces to “track, monitor and warn away” the U.S. destroyer.

The U.S. Navy said on Sunday that the Hopper had “asserted navigational rights in the South China Sea near the Paracel Islands, consistent with international law.”

China claims almost the entire South China Sea, a conduit for more than $3 trillion of annual ship-borne commerce, including parts claimed by the Philippines, Vietnam, Indonesia, Malaysia and Brunei. The Permanent Court of Arbitration in 2016 said China’s claims had no legal basis.