An investigation is under way into a “significant attempt to derail a train” which was carrying about 60 passengers, British Transport Police said today.
The Arriva train crashed into a large metal object on the track close to Llanbradach station, near Caerphilly, south Wales, just after 9pm on Friday.
A BTP spokeswoman said none of the passengers on the Penarth to Rhymney train were injured and they were escorted along the track to continue their journey by coach.
The spokeswoman said: “A large, heavy metal grease pot appears to have caused the obstruction. The impact was so severe it rendered the train disabled.”
She added: “This is considered a significant attempt to derail a train and British Transport Police are treating it as extremely serious.
“The offence of endangering the safety of passengers is punishable with life imprisonment.”
Investigating officers are carrying out an examination of the scene and the train.
Anyone with any information relating to the incident is urged to call BTP on 0800 405040.