"According to the very first preliminary information, about 10 people were killed in the explosion," a source told TASS, noting the exact number of victims was still being established.

Russian President Vladimir Putin expressed his condolences to the victims and is talking to the FSB security services about the investigation, according to state media.

Kremlin spokesman Dmitry Peskov said Putin was in St. Petersburg speaking at an event earlier Monday but that he was now in the nearby city of Strelna.

At least 10 people were killed and 50 injured by at least one explosion in a metro station in St. Petersburg, Russia on Monday, the Russian National Anti-Terrorism Committee confirmed. Interfax is reporting that one of the blasts involved a device filled with shrapnel.

St. Petersburg emergency services report that there were blasts in two metro carriages at two metro stations. All St. Petersburg metro stations have since been closed.

Saint Petersburg is one of the modern cities of Russia, as well as its cultural capital. The Historic Centre of Saint Petersburg and Related Groups of Monuments constitute a UNESCO World Heritage Site. Saint Petersburg is home to The Hermitage, one of the largest art museums in the world. A large number of foreign consulates, international corporations, banks, and businesses have offices in Saint Petersburg.