An explosion at a storage site for unexploded ordnances at a US military base on Japan’s southern island of Okinawa injured four Japanese soldiers, though the injuries are not life threatening, officials said on Monday.

The four soldiers sustained finger injuries while working at a facility that belongs to Okinawa prefecture and temporarily stores unexploded ordnance, mostly from wartime and found on the island, local officials said. 

One of the harshest battles of World War II was fought on Okinawa. Prefectural officials said the injuries were not life threatening, but no other details were immediately known.