The railway line between Inverness and Perth is expected to remain closed after a train derailed during testing.
The incident happened near Dalwhinnie in the Highlands at 3.10am on Saturday.
The train was travelling south when the last two carriages derailed, the Rail Accident Investigation Branch (RAIB) said.
Scotrail confirmed it was not a passenger service and no one was injured.
Work began on Saturday to recover the train but Network Rail said today it would not be completed for Monday’s services.
A spokesman said: “Work is continuing onsite to re-rail the rear power car and coach which were derailed on Saturday.
“Once that process is complete, there will be track and signalling repairs needed before we can reopen the line.
“We’re working as quickly as possible to re-rail the train, but this will not be completed for Monday’s services.”
Services have been disrupted in the meantime. Trains heading north are only able to go as far as Pitlochry and will restart at Aviemore. Southbound trains are stopping at Aviemore and starting again at Pitlochry.
Replacement buses are running in their place.
The Rail Accident Investigation Branch released a statement saying it was looking into the incident.
The agency said: “We are deploying inspectors to gather evidence following the derailment of a test train at Dalwhinnie on the Highland Line in Scotland.
“The train consisted of a short-form HST that was travelling south when the last two vehicles derailed in proximity to points.”
A Scotrail spokesman said customers should continue to check the website and social media channels for more information.