At least ten people were killed in Monday’s blast on a metro train in St Petersburg and 47 people have been injured, Russian news agency Interfax quoted the country’s health minister, Veronika Skvortsova, as saying.

Earlier, the Russian National Anti-Terrorist Committee said nine people had been killed in the blast which happened as a train traveled between two metro stations.

All the more, France announced increasing security at public transport locations in Paris after an explosion killed at least nine people in the St. Petersburg metro tunnel.

The announcement was made by the French interior ministry.

“Following the events in the St. Petersburg metro, and as a precautionary measure, Interior Minister Matthias Fekl has decided to redeploy security means in public transport across the Paris region,” the ministry said in a statement.

“Amid an extremely high terrorism threat, the government continues to take measures to protect the French people.”

On the Petersburg subway attack, Russia’s National Anti-Terrorist Committee said an unidentified explosive device went off on a train that was traveling between two stations.

The committee affirmed that security would be tightened at all critical transport facilities after blast.

Seven of St. Petersburg’s metro stations have been closed and an evacuation was underway. Victory Park, Electrosila, Moscow Gate, Frunzenskaya, Technological Institute, Sennaya Ploshchad, Gostiny Dvor have been shut at the entrance and exit points.

Russian President Vladimir Putin, who was visiting the city on an unrelated trip Monday, said investigators were looking into whether the explosion was a terror attack or if there might have been some other cause.

“The reasons for the explosion are unknown, so it’s too early to talk about it. The investigation will show what happened,” Putin said.

“Naturally, we always consider all options — both domestic and criminal, primarily incidents of a terrorist nature.”

He offered his condolences to the families of the victims.

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. He was expected to hold talks with the Belarusian president Alexander Lukashenko later in the day.

Social media users posted photographs and video from a subway station in the city center, showing people lying on the floor and a train with a mangled door nearby. Frantic commuters reached into doors and windows, trying to see if anyone was there and shouting “Call an ambulance!”