Pakistan Railways on Wednesday said sabotage did not appear to have been a factor in the overnight derailment that killed at least 45 people.
"Apparently there was no sabotage," operations manager Asad Saeed told AFP by phone from company headquarters in the eastern city of Lahore.
"Initial reports said a welded joint on the track broke, due to contraction in the extreme cold," he said. "It sometimes happens in winter."
Army troops were working along with rescuers as the search for more bodies or any other survivors continued nearly 12 hours after the accident.