The detonation of a shrapnel-packed bomb killed up to ten people and injured dozens more in the metro underground railway system in the northern Russian city of St Petersburg on April 3.

The device blew up inside a train travelling between the central Sennaya Ploshchad and Tekhnologicheskiy Institut stations at 2:40 pm local time, security officials said. Another device was reportedly found and deactivated at another station. No one immediately claimed responsibility for the attack.

Russian President Vladimir Putin said all causes, including terrorism, were being investigated. “Certainly, all causes are being considered, both common crime and manifestations of terrorism,” said Putin, who was in St Petersburg for talks with his Belarusian counterpart Alexander Lukashenko.

Photos from the scene posted on social media show injured passengers on the platform and a smoke-filled station. One of the pictures from the scene shows what appears to be carriage doors blown out from the inside.

St Petersburg emergency services initially said there had been two explosions. But a source in the emergency services later told Reuters there had been only one and that the explosion had occurred in a tunnel between the stations.

A spokesman for St Petersburg's governor said at least ten people had been killed and 50 injured. Shortly after, Russia’s National Anti-Terrorist Committee said the death toll was nine, with 20 hurt.

The head of the committee, Andrei Przhezdomsky, confirmed that the explosion was caused by “an unidentified explosive device” but said the exact cause had yet to be determined.

The St Petersburg metro is the 19th busiest in the world, carrying more than 2mn passengers every day. It has not suffered attacks before. All of the city’s metro stations were quickly closed after the bombing, while the Moscow metro also said it was taking additional security measures in case of an attack there.

As he met with Lukashenko, Putin expressed his condolences after the “possible terror attack” and said he had consulted with national security chiefs as a full investigation was launched.

Russia has suffered numerous terrorist attacks in public places in the past, including bombs detonated on metro trains by Chechen separatists. However, since the end of the second Chechen conflict and the installation of Kremlin puppet Ramzan Kadyrov as head of the Chechen Republic there have been far fewer terrorist attacks in the Russian Federation.

The last metro bombing was at Moscow’s Park Kultury metro station in March 2010 that killed 38 people and injured twice as many. In 2009, a bomb exploded on a high-speed train travelling between Moscow and St Petersburg, killing 27 and injuring another 130. Islamist groups claimed responsibility for both attacks.

Recently there have been warnings that Russia’s intervention in Syria on the side of Bashar al-Assad could make Russia a target for the so-called Islamic State. In December, the Russian ambassador to Turkey was shot dead by an off-duty Turkish police officer who shouted “Don’t forget Aleppo” as he pulled the trigger.

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