A fire which broke out on an Italian train carrying football fans has killed four people and injured at least nine.

The train -- taking fans home to the southern city of Salerno -- was in a tunnel at the time of the accident, trapping the passengers inside a carriage.

The cause of the accident is not known, but there have been reports of a smoke bomb going off on the train before the fire.

The Salerno fans were returning from a match that saw their team relegated to the second division.