Russian authorities say at least nine people have been killed and 50 others injured in an explosion on the metro system in the city of St. Petersburg, Russia's second largest city.
St. Petersburg Metro Explosion

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Blast victims lie near a subway train hit by a explosion at the Tekhnologichesky Institut subway station in St.Petersburg, Russia, April 3, 2017.

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A subway train hit by a explosion stays at the Tekhnologichesky Institut subway station in St.Petersburg, Russia, April 3, 2017.

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People carry a subway blast victim into an ambulance after explosion at Tekhnologichesky Institut subway station in St.Petersburg, Russia, April 3, 2017.

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People carry a subway blast victim into an ambulance after explosion at Tekhnologichesky Institut subway station in St. Petersburg, Russia, April 3, 2017.