ScotRail confirmed on social media on Monday that the line remains closed between Blair Atholl and Kingussie, and that replacement transport has been organised for those travelling between Perth and Inverness.
The company added that services from Inverness to Glasgow Queen Street and Edinburgh will terminate at Kingussie and restart from Blair Atholl.
Likewise services from Glasgow Queen Street and Edinburgh to Inverness will terminate at Blair Atholl.
The derailment happened on Saturday, April 10, near Dalwhinnie station at around 3.15am during overnight testing.
It was not a passenger service, and nobody was injured during the incident, ScotRail confirmed.
Regulators, The Rail Accident Investigation Branch said on social media: “RAIB is deploying inspectors to gather evidence following the derailment.
"The train consisted of a short-form HST that was travelling south when the last two vehicles derailed in proximity to points.”