Radical Russian nationalists are thought to be the most likely culprits in a bombing which derailed a Moscow to St Petersburg express train.
'Detectives and investigation staff are working on several angles, however the priority lead is that representatives of extremist nationalist organisations were involved in this terrorist act,' Interfax quoted the source as saying.
A bomb laid on the tracks derailed the train travelling from Moscow to St Petersburg on Monday night, tipping over several carriages and wounding dozens of passengers. No one was killed. The route is one of Russia's busiest.
Radical nationalists are most commonly associated with street attacks on dark-skinned migrant workers, but they have been linked in the past to bomb attacks.
Two nationalists were convicted of blowing up a train in 2005 that was travelling to Moscow from the southern Russian region of Chechnya, which has a majority Muslim population.
