China said on Thursday a U.S. warship had illegally entered its territorial waters in the South China Sea, and was expelled by its forces, an assertion the United States denied, in the latest exchange of salvos over Beijing’s claims in the busy waterway.

In a statement, the Chinese military’s Southern Theatre Command said the USS Curtis Wilbur entered the waters near the Paracel islands without permission, adding that its ships and planes followed the U.S. vessel and “expelled” it.

It added that China opposed the U.S. action, which it said violated its sovereignty and undermined regional peace and stability.

However, the U.S. Navy’s 7th Fleet said the vessel “asserted navigational rights and freedoms” near the Paracel islands, over which China, Taiwan and Vietnam all claim sovereignty.

The Chinese military’s comments about the mission were false, it added.

“USS Curtis Wilbur was not ‘expelled’ from any nation’s territory,” it said.

“USS Curtis Wilbur conducted this Freedom of Navigation Operation (FONOP) in accordance with international law and then continued on to conduct normal operations in international waters.”

The South China Sea has become one of many flashpoints in the testy relationship between China and the United States, with Washington rejecting what it calls unlawful territorial claims by Beijing in the resource-rich waters.

U.S. warships have passed through the South China Sea with increasing frequency in recent years, in a show of force against the Chinese claims.