British Transport Police are investigating an incident on a train bound for the north-east.
The force has asked ScotRail to provide CCTV footage after reports of antisocial behaviour on the 8.40pm service from Glasgow Queen Street to Aberdeen on Saturday.
The train guard was reportedly subjected to verbal abuse by a group of passengers on the service.
The emergency brake was also reportedly applied.
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The train was met by officers when it arrived in Aberdeen just after midnight, nearly an hour after its scheduled arrival time.
No arrests have yet been made.
A BTP spokesman said: “We are aware of a report of antisocial behaviour on board the 8.40pm train from Glasgow Queen Street to Aberdeen on Saturday evening.
“Nobody has been arrested, but CCTV footage from the train has been requested.”