Railway Minister D.V. Sadananda Gowda Wednesday said it was too early to comment on the cause of the Delhi-Dibrugarh Rajdhani Express derailment in Bihar."It is not proper to say anything on the cause of the accident as I am on my way to the site," Gowda told the media before leaving for Chhapra."I will see and observe things and discuss with railway officials and district officials to know the cause of the accident."Four people were killed and nine injured when nine coaches of the train ran off the tracks near Chhapra early Wednesday.