MOSCOW – A rush-hour subway train derailed Tuesday in Moscow, killing 20 people and sending 150 others to the hospital, many with serious injuries, Russian officials said.

The Russian capital’s airports and transit systems have been hit by several terrorist attacks in the past two decades but multiple officials on Tuesday vigorously dismissed terrorism as a possible cause.

The Moscow Metro is one of the most famous subway systems in the world, known for its palatial interiors with mosaics, chandeliers and marble benches. Park Pobedy, where the derailment occurred, is Moscow’s deepest metro station – 84 meters (275 feet) deep, which was making the rescue particularly difficult. The station serves the vast western park where Russia’s World War II museum is located.

Russian emergency officials initially said several cars derailed in the tunnel after a power surge Tuesday morning triggered an alarm that caused the train to stop abruptly. But Vladimir Markin, spokesman for the Investigative Committee, told reporters later that a power surge was not the issue and that investigators were considering a fault in the train cars or the sinking of the roadbed among the possible causes.

Of the 150 people reported injured, at least 50 were in grave condition, Moscow health officials said. Over 1,100 people were evacuated from the train, which was stuck between two stations, in a rescue operation that has already lasted at least seven hours.

By late afternoon, rescuers had recovered seven bodies and were working to extract 12 more trapped in two wrecked train cars, said Alexander Gavrilov, deputy chief of the Moscow emergency services. One woman taken from the scene died in a Moscow hospital.

In a video issued by the Emergency Situations Ministry, rescuers could be seen working inside the tunnel where several wrecked train cars looked almost coiled, occupying the entire width of the tunnel. Workers were trying to force open the mangled doors of one car to retrieve dead bodies.

Earlier photos on social media showed passengers walking along the tracks inside the dimly lit tunnel.

Mayor Sergei Sobyanin told reporters that unnamed officials will not only be fired but also investigated and charged in the aftermath of the deadly derailment. He refused to elaborate on what charges they could face.

Traffic between the stations is likely to be suspended for at least two days, he said.

Dozens of injured people were carried out of the subway station on stretchers. Paramedics carried one woman covered with a blanket to the lawn by the famous Triumphal Arch and put her on a medical helicopter.

Several survivors sat on the sidewalk near the station’s entrance in an apparent state of a shock, drinking water supplied by authorities on a hot summer day.

One man with a bloody cut on his brow told Rossiya 24 television outside the Park Pobedy station that he felt a jolt and the train abruptly came to a halt.

“There was smoke and we were trapped inside,” he said. “It’s a miracle we got out. I thought it was the end.”

While technical glitches are regular occurrences in the Moscow Metro, the city’s subway hasn’t seen deadly accidents in decades.

Terrorism is another matter. More than 100 people have been killed in bombings on Moscow’s subway trains or near stations since 2000, including two bomb blasts on the same day in 2010 that killed a total of 40 people.

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