At least 25 people have been killed and 102 others injured in the derailment of a Russian express train on Friday, local media quoted emergency officials as saying.
Four carriages of the Nevsky Express traveling from Moscow to St. Petersburg went off the tracks at 9:30 p.m. Moscow time (1830 GMT) near the town of Bologoye on the border between the Tver and Novgorod regions, local media reported.
Twenty-five people were killed, including two who died in the hospital, said Emergency Situations Minister Sergei Shoigu, based on reports from officials at the scene, during a meeting televised by Vesti-24 television.
Shoigu said 87 of those injured were sent to hospitals in the area, and another 15 were taken to St. Petersburg for medical treatment.
Twenty-seven people who are known to have been on the train remain unaccounted for, the minister added.
Russian Railways said the reason behind the accident was not yet clear, but the derailment could have been caused by an act of terrorism.
The Interfax news agency cited an unnamed source with Moscow's law enforcement agencies as saying that a hole one meter in diameter was found
near the scene of the accident.
"Witnesses heard a loud bang before the accident. All this could point to a possible attack," the source said.
A bomb attack hit the same line in 2007, injuring dozens of passengers.
Russian President Dmitry Medvedev has instructed Shoigu to take all necessary measures to extend assistance to those affected, the Kremlin said.
Medvedev has also ordered federal security service FSB chief Alexander Bortnikov and Prosecutor-General Yuri Chaika to investigate into the cause of the disaster.
Russian Railways President Vladimir Yakunin rushed to the scene, where ambulances, rescuers, FSB officers, law enforcers, and railroad specialists are working.
The railroad monopoly said trains will move along a bypass route after the accident to keep railroad communication between the two largest Russian cities running.
The route between Moscow and St. Petersburg, Russia's second largest city, is heavily traveled by tourists and business people.
The 14-carriage train was carrying 633 passengers and 20 railway personnel when the incident took place, the emergency situations ministry said.