China has “enforced maritime management and exercised sovereign jurisdiction” over an uninhabited reef in the disputed South China Sea, planting the country’s flag on the tiny sand bank just kilometers from a key Philippine military outpost. Photographs released by Chinese state-run media on Saturday showed China Coast Guard officers unfurling the flag as part of an effort to effectively seize Sandy Cay reef, which Beijing calls Tiexian Jiao, earlier this month. The reef, located in the flash point Spratly Island chain, is also claimed by Taiwan, Vietnam and the Philippines. Sandy Cay also sits just over 3 kilometers from Thitu...