The United States has sailed a warship near two of China’s man-made islands in the disputed South China Sea, the latest in a series of recent moves by the U.S. military in the strategic waterway and in the diplomatic arena amid rising tensions between Washington and Beijing.

The guided-missile destroyer USS Decatur on Sunday sailed within 12 nautical miles (22 km) of Gaven and Johnson reefs in the Spratly Islands as part of what the U.S. Navy calls “freedom of navigation operations” (FONOPs). The operations are meant to enforce the right of free passage in international waters under international law. The two islets are also claimed by Taiwan, Vietnam and the Philippines.

Both outposts are among seven in the Spratly chain that China has built up, with some transformed from so-called high-tide elevations entitled to 12 nautical mile territorial seas into garrisons with massive radar installations, scores of buildings and military-grade runways.