Tokyo: Four Japanese soldiers were injured in an explosion at an unexploded ordnance storage facility at a US military base on the southern Japanese island of Okinawa. Officials said the injured were out of danger. Details of the accident The explosion occurred at a facility run by Okinawa Prefecture, where unexploded ordnance from World War II is temporarily stored. The injured soldiers suffered injuries to their fingers while working at the facility. Okinawa was the scene of one of the fiercest battles of World War II. The cause of the explosion, according to the Japanese Self-Defense Force (SDF), was when a device suddenly exploded while soldiers were checking weapons. NHK television reported that the explosion occurred while soldiers were trying to remove rust. The US Air Force said the explosion occurred at an ammunition storage facility at Kadena Air Base and that no US soldiers were involved. Investigation and background SDF officials are investigating the cause of the explosion. This is believed to be the first accident since the establishment of the Japanese military's unexploded ordnance disposal unit in 1974. In Japan, especially in Okinawa, there are still about 1,856 tons of unexploded bombs left by the US military, often found on construction sites. Last October, an unexploded US bomb exploded at a commercial airport in southern Japan, leaving a large crater and suspending dozens of flights.