An explosion at a storage site for unexploded ordnance inside the U.S. military’s Kadena Air Base in Okinawa on Monday injured four Japanese soldiers, according to reports. 

According to Japanese media, the explosion occurred while Japan’s Ground Self-Defense Force (JSDF) members were preparing to safely dispose of unexploded ordnance. 

Reports indicate the depot serves as a temporary storage site, primarily holding leftover unexploded munitions from World War II.

Local officials said the injuries obtained by the soldiers were not serious. Meanwhile, The U.S. Air Force said no injuries were reported among U.S. personnel.

Okinawa was the site of a major battle in 1945 and was heavily bombed by the U.S. military. Many unexploded bombs are still found around the island. More than 2,000 tons have been removed, but about 1,856 tons are believed to remain buried.

In a similar incident last October, a wartime U.S. bomb exploded at a commercial airport in southern Japan, creating a crater and halting flights.