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MOSCOW — An explosion tore through a subway train in the Russian city of St. Petersburg on Monday, killing 11 people and injuring dozens more, officials said.

The blast struck while Russian President Vladimir Putin was visiting the country's second-largest city, which is where he was born.

The train was between two stations when the explosion happened, according to the country's National Anti-Terrorism Committee.

"As a result there are victims, dead and wounded," the committee said in a statement.

A second explosive device was found at another station but it did not detonate, according to Andrei Przhezdomsky, head of the committee's information center.

Valery Parfenov, director of the Saint-Petersburg I.I. Dzhanelidze Research Institute of Emergency Medicine, where many of the wounded were being treated, told the REN TV channel that the explosives were filled with ball bearings, screws and pieces of metal.

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Russian Health Minister Veronika Skvortsova said in a live interview with Russia 24 television that the death toll had risen to 11, with two succumbing to their wounds in the hospital. Another 39 remained hospitalized, Skvortsova said.

More victims may still be pulled from the wreckage, authorities said.

The explosion happened at around 2:40 p.m. local time (7:30 a.m. ET), according to the National Anti-Terrorism Committee.

Emergency personnel help an injured person outside Sennaya Ploshchad metro station in St. Petersburg on Monday. Anton Vaganov / Reuters

Images circulated on social media showing a mangled train car, bodies lying on the ground and emergency vehicles parked outside what appeared to be an entrance to the station. None of these images have been verified.

The blast happened when the train was between the Sennaya Ploschad and Tekhnologichesky Institute subway stations. The second device was found at Ploshchad Vosstaniya station, officials said.

According to Sputnik, Putin said that "all possible causes of the explosion in the St Petersburg metro are being considered, including terrorism."

Russia's FSB intelligence agency was investigating the explosion.

PHOTOS: Explosion Rocks Russian Subway

The subway was closed for several hours while authorities checked the system for other threats. It was reopened Monday night with tighter security, officials said.

In a phone call with Putin, President Donald Trump offered condolences, the White House said in a statement on Monday night.

Trump also pledged to support Russia's response to the attack and its pursuit of justice, the statement said.

"Both President Trump and President Putin agreed that terrorism must be decisively and quickly defeated," the statement said.

Alexander Smith reported from London.