PHNOM PENH, Cambodia (AP) — A huge explosion in southwestern Cambodia over the weekend that killed 20 soldiers at an army base appears to have been an accident caused by mishandling of ammunition by troops, a senior military official said Tuesday.

The Saturday afternoon blast in Kampong Speu province also destroyed military vehicles and four buildings at the base, and damaged homes in a nearby village.

Army spokesperson Maj. Gen. Mao Phalla said the soldiers were transferring ammunition from trucks into a storage facility when the blast occurred, killing them instantly. He said another 11 people, including soldiers and nearby villagers, were slightly injured, mostly from debris from the damaged buildings, not shrapnel.

Cambodia held a mass funeral on Sunday for those killed in the explosion.

The initial but still not official theory was that the soldiers were unloading ammunition from a truck and stacking it on the ground before moving it into the storage facility, causing one item to explode, he said. That set off a chain reaction, added Mao Phalla.