Probe into metro derailment

President Putin, who is currently in Brazil, offered his condolences on Tuesday and ordered the head of the Investigative Committee, Vladimir Bastrykin, to launch a criminal investigation into the derailing, the Kremlin said.

The investigative body said that three wagons derailed near the Park Pobedy station at 8:35 am (0435 UTC), when the train was travelling at a speed of 70 kilometers per hour (43.5 mph). At least 21 people were killed and more than 150 injured. Officials said that those killed were pulled out of the train's first two wagons. Some 50 people remain in grave condition.

Photos and video from the scene showed several wagons twisted and piled up, occupying the entire width of the tunnel. Rescue efforts lasted about seven hours as the Park Pobedy metro station is Moscow's deepest at 84 meters (275 feet) below the surface. Overall, some 1,100 passengers were rescued from the tunnel.

Cause unknown

The exact cause of the accident was not immediately clear.

"The most likely explanation is that this catastrophe was technical," said committee spokesman Vladimir Markin. He added that an earlier theory, that a sudden power surge triggered an alarm, had not been confirmed.

The Moscow Metro ranks among the world's busiest commuter systems carrying about 9 million passengers per day through the capital. The underground system is also famous for its grand interiors with mosaics, chandeliers and marble benches. It has been the target of several terrorist attacks, most recently in 2010, when two suicide bombings killed 40 people. However, the Investigative Committee has ruled out a terrorist attack.

It was believed to be the worst accident in the Moscow Metro's nearly 80-year history. In 1982, 15 people were killed when an escalator collapsed.

hc/kms (Reuters, AP, dpa)