A U.S. Navy destroyer sailed near islands claimed by China in the South China Sea on Wednesday, the U.S. military said, a move likely to anger Beijing at a time of tense ties between the world’s two largest economies.

The busy waterway is one of a growing number of flashpoints in the U.S.-China relationship, which include a trade war, U.S. sanctions and Taiwan. Reuters reported on Tuesday that China had denied a request for a U.S. Navy warship to visit the Chinese port city of Qingdao.

The U.S. Navy destroyer Wayne E. Meyer carried out the operation, traveling within 12 nautical miles of Fiery Cross and Mischief Reefs, Commander Reann Mommsen, a spokeswoman for the U.S. Navy’s Seventh Fleet, told Reuters.

Mommsen added that the operation was done to “to challenge excessive maritime claims and preserve access to the waterways as governed by international law.”

The U.S. military operation comes amid an increasingly bitter trade war between China and the United States which sharply escalated on Friday, with both sides leveling more tariffs on each other’s exports.

The U.S. military has a long-standing position that its operations are carried out throughout the world, including areas claimed by allies, and they are separate from political considerations.

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

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