VIDEO:At least ten dead left explosion in the subway of St. Petersburg

At least 10 people were killed and 50 injured in an explosion on an underground train in the Russian city of St. Petersburg, it was reported Monday. President Vladimir Putin expressed his condolences for the victims and said they are investigating whether it was a terrorist act.
Russian agencies Tass and Interfax reported the death toll of 10.

Authorities have already strengthened security in the transportation system and closed all subway stations.

The National Anti-Terrorism Committee reported that an unidentified explosive device detonated on a train traveling between two stations. Maxim Liksutov, deputy mayor of Moscow, told Interfax that Moscow authorities reinforced security in the subway of the Russian capital.

Users on social networks posted pictures of a subway station in the center of the city, showing people lying on the ground and a train with a shattered door.

The president expressed his condolences for the victims. Putin was visiting the city.