In this frame grab provided by the Russian Ministry for Emergency Situations shows frame grab from a video showing rescue teams working inside the tunnel where several cars of the wrecked train look almost coiled, occupying the entire space of the tunnel of Moscow subway in Moscow, Russia, on Tuesday, July 15, 2014. Workers were seen trying to force open the mangled doors of the car where dead bodies are supposed to be. (Photo by AP Photo/Russian Emergency Situation Ministry)

Paramedics, a police officer and a voluenteer carry an injured man out from a subway station after a rush-hour subway train derailment in Moscow, Russia, on Tuesday, July 15, 2014. A rush-hour subway train derailed in Moscow Tuesday, killing about 20 people and injuring at least 106, emergency officials said. Several cars left the track in the tunnel after a power surge triggered an alarm, which caused the train to stop abruptly. (Photo by Ivan Sekretarev/AP Photo)

Paramedics carry an injured man out from a subway station after a rush-hour subway train derailment in Moscow, Russia, on Tuesday, July 15, 2014. (Photo by Ivan Sekretarev/AP Photo)

In this frame grab provided by the Russian Ministry for Emergency Situations shows frame grab from a video showing rescue teams working inside the tunnel where several cars of the wrecked train look almost coiled, occupying the entire space of the tunnel of Moscow subway in Moscow, Russia, on Tuesday, July 15, 2014. (Photo by AP Photo/Russian Emergency Situation Ministry)

Paramedics carry an injured woman out from a subway station after a rush-hour subway train derailment, to be transported by a medical helicopter in Moscow, Russia, on Tuesday, July 15, 2014. (Photo by Ivan Sekretarev/AP Photo)

Members of the emergency services wait outside a metro station following an accident on the subway in Moscow July 15, 2014. (Photo by Sergei Karpukhin/Reuters)

Russian rescue workers transport an injured passager to an ambulance from “Park Pobedy” metro station, where three carriages derailed in Mocow, Russia, July 15, 2014. (Photo by Yuri Kochetkov/EPA)

Members of the emergency services enter a metro station following an accident on the subway in Moscow July 15, 2014. (Photo by Sergei Karpukhin/Reuters)

Members of the emergency services carry an injured passenger outside a metro station following an accident on the subway in Moscow July 15, 2014. (Photo by Sergei Karpukhin/Reuters)

Members of the emergency services carry an injured passenger outside a metro station following an accident on the subway in Moscow July 15, 2014. (Photo by Sergei Karpukhin/Reuters)

Members of the emergency services stand near a map of train lines outside a metro station following an accident on the subway in Moscow July 15, 2014. (Photo by Sergei Karpukhin/Reuters)

Members of the emergency services carry an injured passenger outside a metro station following an accident on the subway in Moscow July 15, 2014. (Photo by Sergei Karpukhin/Reuters)

Paramedics, a police officer and a volunteer carry an injured man out from a subway station after a rush-hour subway train derailment in Moscow, Russia, on Tuesday, July 15, 2014. (Photo by Ivan Sekretarev/AP Photo)

In this frame grab from video provided by the Russian Ministry for Emergency Situations, rescue teams work inside the tunnel in Moscow where a rush-hour subway train derailed Tuesday, July 15, 2014, killing at least 20 people and sending 150 others to the hospital, many with serious injuries, Russian officials said. Officials vigorously dismissed terrorism as a possible cause. (Photo by AP Photo/Russian Emergency Situation Ministry)

Paramedics carry an injured woman from a subway station after a rush-hour subway train derailment to a medical helicopter in Moscow, Russia, on Tuesday, July 15, 2014. A rush-hour subway train derailed in Moscow Tuesday, killing 20 people and injuring at least 150, emergency officials said. Several cars left the track in the tunnel after a power surge triggered an alarm, which caused the train to stop abruptly. (Photo by Ivan Sekretarev/AP Photo)

Paramedics treat injured passengers on a grass verge as several subway cars on a metro train derailed in Moscow, on July 15, 2014. (Photo by Mikhail Japaridze/AFP Photo)

Paramedics carry an injured woman from a subway station after a rush-hour subway train derailment to a medical helicopter in Moscow, Russia, on Tuesday, July 15, 2014. (Photo by Ivan Sekretarev/AP Photo)