Photo gallery: St. Petersburg subway explosion

People light candles and lay flowers outside Sennaya Ploshchad metro station after an explosion, in St. Petersburg, Russia, April 3, 2017. Russia’s National Anti-Terrorist Committee said that the explosions hit a train between Sennaya Ploshchad and Tekhnologichesky Institut stations.

A man lays flowers in memory of victims of the blast in the St. Petersburg metro at a memorial stone reading Leningrad by the Kremlin wall in central Moscow on April 3, 2017.

People talk on their phones outside Tekhnologichesky Institute metro station after an explosion, in St. Petersburg, Russia, April 3, 2017. According to reports, at least 10 people were killed and dozens injured in an explosion in the city’s metro system. The cause of the blast was not immediately known.

People react outside Technological Institute metro station in St. Petersburg on April 3, 2017. About ten died and dozens were injured Monday after an explosion rocked the metro system in Russia’s second largest city St. Petersburg, according to authorities, who were not ruling out a terror attack.

Police and emergency services personnel carry an injured person on a stretcher outside Technological Institute metro station in St. Petersburg on April 3, 2017.

An injured man is helped by medics outside Technological Institute metro station in Saint Petersburg on April 3, 2017.

Medics help an injured woman outside the Technological Institute metro station in St. Petersburg on April 3, 2017.

Emergency services personnel walk at the entrance to the Technological Institute metro station in St. Petersburg on April 3, 2017. Around 10 people were feared dead and dozens injured Monday after an explosion rocked the metro system, according to authorities, who were not ruling out a terror attack.

Emergency services personnel and vehicles are seen at the entrance to Technological Institute metro station in Saint Petersburg on April 3, 2017.

Police officers guard the area at the entrance to Technological Institute metro station in St. Petersburg, Russia, on April 3, 2017.

Emergency vehicles and a helicopter are seen at the entrance to Technological Institute metro station in Saint Petersburg on April 3, 2017.