Egypt has charged three railway workers with involuntary manslaughter after two trains collided south of Cairo, killing 18 people.

The office of the general prosecutor says the two conductors and a third man who was supposed to be monitoring the tracks but allegedly abandoned his post were also charged with damaging public interest Monday. All three were ordered jailed.

Saturday's crash was caused by an errant water buffalo that wandered onto the tracks. The first passenger train stopped after hitting the buffalo and was then rear ended by a second train going at full speed.

Egypt has a poor safety record on its railways, and there are several fatal accidents each year, usually blamed on poorly maintained equipment.