One sailor was killed after an explosion on a naval vessel off the southern South Korean coast on Tuesday, Yonhap reports. The accident happened at around 12:20pm on a 1,500-ton Masan naval frigate about 25 nautical miles south of an island off the southern coastal city of Tongyeong, about 380km south of Seoul. The wounded sailor, identified as a 21-year-old Petty Officer 1st Class surnamed Lee, suffered a serious head injury and was later pronounced dead, according to the military. The explosion was probably caused as he was removing ammunition from a 30-mm gun to prepare for live-fire drills, the Navy said. The investigation will start as soon as the vessel docks at a port in the southern city of Changwon.