Police in the southern Russian republic of Dagestan have launched a criminal investigation into a terrorist attack on Thursday evening in which 14 empty freight train carriages derailed due to an explosion.
The blast damaged a small section of the tracks and caused a 30-centimeter-deep crater.
Though no one was killed or injured, almost 700 people remain unable to continue their journeys.
Demolition experts are working at the scene.
This is second explosion on the tracks in Makhachkala in a month.
In February, a suspected terrorist blew himself up while trying to plant a bomb.