"Guided-missile destroyer USS Decatur conducted a freedom of navigation operation," an official told AFP. "Decatur sailed within 12 nautical miles of Gaven and Johnson reefs in the Spratly Islands."

The official said all US military operations in the area "are designed in accordance with international law and demonstrate that the United States will fly, sail and operate wherever international law allows."

The 12-mile distance is commonly accepted as constituting the territorial waters of a landmass. Beijing claims all of the Spratly chain.

There was no immediate reaction from China, but a similar US operation in July, involving the disputed Paracel islands, prompted a furious Beijing to deploy military vessels and fighter jets.

The Paracels, north of the Spratly Islands, are claimed by China, Taiwan and Vietnam.

On May 25, the guided-missile destroyer USS Dewey sailed less than 12 nautical miles from a reef in the Spratly archipelago.

China claims nearly all of the South China Sea, though Taiwan, the Philippines, Brunei, Malaysia and Vietnam all claim parts of it.

Further angering those countries, and the US, Beijing has moved aggressively to build reefs into artificial islands capable of hosting military planes.

US-Chinese relations have been strained on multiple levels since Donald Trump became president in 2017. A trade war launched by Trump has infuriated Beijing, as did his authorization of a $1.3 billion arms sale to Taiwan, which China considers a rebel province.