BBC News reports two U.S. B-52 bomber planes have flown near artificial islands built by China in disputed areas of the South China Sea, the Pentagon has said. Their mission continued despite being warned by Chinese ground controllers. The incident comes ahead of a visit by US President Barack Obama to a summit in Manila next week, which China's President Xi Jinping will also attend. China is locked in maritime territorial disputes with several neighbors in the South China Sea. It claims a large swathe of the resource-rich area and has been aggressively reclaiming land and building facilities on reefs, which the U.S. and others oppose.