
Four wagons of the Nevski Express linking the two cities came off the tracks late on Friday evening in the Novgorod region, a railways official told the Ria-Novosti news agency.
Russia's state-run Itar-Tass news agency quoted the emergencies ministry and a railway official as saying that 22 people were dead and 54 others injured.
A unnamed security official was quoted by the Interfax news agency as saying that a one metre-diameter crater was found near the scene of the disaster.
"Witnesses say they heard a loud bang before the accident. This could be proof of an attack,'' the source said.
A railways official also told Itar-Tass that "an attack is one of the possibilities'' being looked at by the police.