Dehnow, Iran ? Bulldozers digging graves in this tiny Iranian village Thursday drowned out the wails of mourners waiting to bury loved ones killed when a runaway train derailed at more than 90 mph and exploded, killing 320 people and injuring hundreds more.

The provincial governor said negligence or brake failure probably caused 51 train cars to roll down the tracks before dawn Wednesday, picking up speed for 31 miles until all but three derailed, caught fire and exploded several hours later.

Many of the dead were firefighters who had nearly extinguished the blaze when gasoline, fertilizer and industrial chemicals in the freight cars detonated. Other victims were villagers whose clay homes collapsed from the force of the blast. About 460 people were injured.

In this village near the train tracks, women clutched their black, all-covering chadors and wailed near the bodies of eight victims. Men sat in the dirt nearby, holding their heads in grief. An old man prayed, bending down and touching his forehead to the ground.

“I don’t want to live, I have lost everything,” said a sobbing Hossein Ghassemabadi, whose son and daughter-in-law were killed. “She was pregnant. I was waiting to see my grandchild.”

Others tried to console him as he beat his chest and face.

The train, with no one on board, was loaded with gasoline, fertilizer, sulfur and cotton when it somehow started rolling out of a railyard before dawn Wednesday. It traveled 31 miles before hitting a sharp turn at the next station. There, all but three cars derailed, with some catching fire.