St Petersburg attack: What we know
A bomb in a train in the Russian city of St Petersburg killed 14 people and injured 51 others on Monday. A suspect has been identified as Akbarzhon Jalilov, a naturalised Russian national born in Kyrgyzstan in 1995, according to the Kyrgyz security service.
How did it happen?
The bomb went off at around 14:30 local time (11:30 GMT) after a train left Sennaya Ploshchad station, heading south for Tekhnologichesky Institut on the blue, north-south metro line.
Initial reports spoke of two bombs but it gradually became clear that there was a single blast, possibly in the third carriage of the train.
The names of the victims have yet to be confirmed by the authorities. The wounded were being treated in four hospitals.
Although the explosion happened in between the two stations the driver continued to Tekhnologichesky Institut to enable victims to be helped more easily. Russia's investigative committee said this decision may have helped prevent further losses.
The St Petersburg metro was shut down and three days of mourning declared. Traffic in surrounding streets and in much of central St Petersburg was brought to a standstill for hours, and volunteers offered lifts via social media to people trying to get home.
At the time of the explosion President Vladimir Putin was just outside Russia's second city, meeting Belarus President Alexander Lukashenko at the Konstantin palace in Strelna.
What caused the explosion?
Early indications were that the bomb was an improvised device made out of the explosive TNT and was possibly hidden in a briefcase close to the carriage doors. Pictures from the scene showed mangled doors and bodies on the floor of the platform.
Minutes later another device was found propped up against a wall at another city metro station, Ploshchad Vosstaniya. That was safely defused and reports said it contained 1kg of TNT, more than used in the original blast.
Prime Minister Dmitry Medvedev described the blast as a "terrorist act" and Russia's investigative committee said it was opening a criminal inquiry under article 205 of the criminal code which refers specifically to terrorist acts. The committee said that all other possibilities were being investigated too.
Who is the suspect?
Details are still emerging about the identity of the suspect. Kyrgyzstan's security service said the man it named as the suicide bomber, Akbarzhon Jalilov, was born in Osh, the country's second-largest city, and obtained Russian citizenship. But the information has not been confirmed yet by Russian authorities.
No group has said it carried out the attack.
Has Russia been attacked before?
Russia's transport infrastructure has been targeted in several occasions.
◾In 2013, suicide bombers killed 31 people in consecutive attacks in Volgograd, on the central station and a trolleybus
◾In 2011, a bombing at Domodedovo airport in Moscow claimed 35 lives
◾In 2010, 38 people were killed in an attack on the Moscow metro by two female suicide bombers
◾In 2009, Islamist militants from the North Caucasus blew up the Nevsky express train from Moscow to St Petersburg, killing 27 people. Two years earlier another express train on the same line was derailed by a bomb.