Commander Reann Mommsen, a spokeswoman for the U.S. Navy’s Seventh Fleet, told Reuters that the destroyer Wayne E. Meyer challenged territorial claims in the operation, including what she described as excessive Chinese claims around the Paracel Islands, which are also claimed by Taiwan and Vietnam.

“…China has attempted to claim more internal waters, territorial sea, exclusive economic zone, and continental shelf than it is entitled under international law,” Mommsen said.

The People’s Liberation Army’s Southern Theater Command said in a statement that the Wayne E. Meyer had entered waters near the Paracels without the permission of the Chinese government

Chinese forces were mobilized to monitor the ship and warn it to leave, the statement said, adding the United States was harming China’s sovereign rights with its repeated patrols in the South China Sea.

“We again stress that China has irrefutable sovereignty over the islands of the South China Sea and their nearby waters. No form of provocation by foreign military ships and aircraft can change this fact.”

The timing is extremely awkward, as the two look to try and resolve a bitter trade dispute.

The United States on Thursday welcomed China’s renewed purchases of U.S. farm goods while maintaining the threat of tariff hikes as the world’s two largest economies prepared the ground for talks aimed at breaking the logjam in their trade war.

China and the United States have traded barbs in the past over what Washington has said is Beijing’s militarization of the South China Sea by building military installations on artificial islands and reefs in disputed waters.

China’s claims in the South China Sea, through which about $5 trillion (£4.02 trillion) in ship-borne trade passes each year, are contested all or in part by Brunei, Malaysia, the Philippines, Taiwan and Vietnam.

Beijing says its construction is necessary for self-defence and that the United States is responsible for increasing tensions by sending warships and military planes close to islands that Beijing claims.