China's military said a US warship had "illegally" entered waters near the Second Thomas Shoal in the South China Sea, which is claimed by China, the Philippines and others. China's Southern Theater Command said it had sent naval forces to follow and monitor the USS Gabrielle Giffords, accusing the US of raising tensions. The US Navy rejected China's accusation, saying the USS Giffords was conducting routine operations in international waters consistent with international law. China claims almost the entire South China Sea despite a 2016 tribunal ruling that its claims have no legal basis. According to the 2016 ruling, the Second Thomas Shoal lies entirely within the Philippines' exclusive economic zone.