The Jaffar Express, which was going from Quetta to Rawalpindi, had about 700 people on board.
The driver saw a suspicious object attached to the tracks near Kolpur yesterday and stopped the train, security officials said.
"The driver stopped the train and informed Pakistan Railway officials about the object," a police official said.
A bomb disposal squad sent to the site confirmed that the suspicious object was an improvised explosive device, he said.
The IED was later defused by the bomb disposal squad.
Officials said the driver