Chinese ships on Monday entered waters at the center of a heated territory dispute with Japan. The move prompted an official protest from Japan as the two countries continue to duke it out over a clutch of mostly uninhabited islands in the East China Sea. Two of the Chinese ships were civilian vessels on a “rights defense” tour, according to Chinese media. Tensions came to a head earlier this month after Japan purchased the islands outright, a decision met with protests across China. “In recent days, Japan has constantly provoked incidents concerning the Diaoyu islands issue, gravely violating China’s territorial sovereignty,” Chinese media said Monday.