The crash happened late on Sunday when several carriages of the Islamabad Express travelling between Rawalpindi and Lahore derailed in a hilly area near Jhelum city. Up to 40 people were injured.
Ishaq Khakwani, the railways minister, said: "It is almost confirmed now that it is an act of sabotage."
A senior security official said the track was damaged before the train passed on its run from Rawalpindi to Lahore, and that tools apparently used for the job, including spanners, were left at the scene and that the fish plates that join different rail sections were open.
Khakwani said there are "several elements" who could be involved in tampering with the rails. "It could be internal, it could be external," he said.
The minister said the suspected sabotage was in a "technically important" area. "Such a derailment in a hilly area could have caused greater loss but luckily there were not many casualties," he said.
He said the repair work was under way and rail traffic was likely to resume on Monday afternoon.
There was no claim of responsibility for the incident.
Pakistan suffered its worst train crash in a decade last July, when a train driver misinterpreted a signal and hit another train at a station.