Pakistani authorities say they suspect Sunday's train crash in eastern Punjab was the result of sabotage.
More than 600 people were on board the train
At least six people died and 40 others were injured when a train travelling to Lahore from Rawalpindi plunged down an embankment near the city of Jhelum.
Federal railway minister Ishaq Khakwani said preliminary investigations suggested a "well-planned act of sabotage" caused the train to derail.
He did not, however, say who might have been behind any such attack.
"It is almost confirmed now that it is an act of sabotage. The evidence says it is sabotage," Mr Khakwani said.
The minister told the BBC that nuts and bolts from a large section of track near a sharp bend had been removed with the intention to cause maximum casualties.
There were more than 600 passengers on the ill-fated train - one of Pakistan's fastest.
Mr Khakwani said it was a sheer miracle that most of them survived.
The minister said "internal or external elements" could be involved in tampering with the railway track.
The train toppled from the tracks in a remote mountain area and troops had to use another train to access the site.
The BBC's Zaffar Abbas in Islamabad says there have been several attempts in recent months to blow up railway tracks and other state installations in the troubled province of Balochistan.
But it is the first time in many years that a passenger train has been targeted in any other part of the country.
Hundreds of people have died in recent years on Pakistan's railways.
More than 130 people were killed near the southern town of Ghotki last July, in Pakistan's worst train disaster in at least a decade.
Correspondents say casualty figures are often so high because trains are packed with far greater numbers than they were designed for and that signalling faults or poorly maintained tracks are often the cause.