The U.S. Navy has sent warships on two occasions in recent days near islands claimed by Beijing in the disputed South China Sea, the military told The Japan Times on Friday.

The so-called freedom of navigation operations (FONOPs) on Wednesday and Thursday came amid rising tensions between the two powers, and just days after China demanded the U.S. military "stop flexing muscles" in the strategic waterway.

On Wednesday, the littoral combat ship USS Gabrielle Giffords traveled within 12 nautical miles (22 km) of Mischief Reef in the Spratly chain, Cmdr. Reann Mommsen, a spokeswoman for the U.S. Navy's 7th Fleet said. And on Thursday, the destroyer USS Wayne E. Meyer challenged restrictions on innocent passage in the Paracel Islands, north of the Spratlys, Mommsen said.