At least 11 people were killed and 51 others were injured in a bomb blast which occurred on St Petersburg metro on April 3, 2017. The explosion tore through a train that was traveling in Russia's second-largest city. Soon after the attack, Russian Prime Minister Dmitry Medvedev described the attack as a "terrorist act." The perpetrators of the terrorist attack fled after the act.
The terrorist attack has raised key questions. First, who is behind the terrorist attack? Second, is Russia's role in Syria endangering the country? Third, is there a Chechen separatist angle to the terrorist attacks?
The blast occurred around 2.30 in the afternoon as the train was traveling in a tunnel from Sennaya Ploshchad to Tekhnologichesky Institut station in the city.
Tekhnologichesky Institut is a cross-platform interchange station of the Saint Petersburg Metro. Following the attack, city's metro system has been shutdown.
Bodies were seen strewn across the station platform outside the train, while rescuers carried injured victims out of the station.
The Anti-Terrorism Committee said no outfit has claimed responsibility for the attack so far. A spokesman for the National Anti-Terrorism Committee said the blast was caused by an unidentified explosive device in one of the train's cars.
President Vladimir Putin who was present in St Petersberg when terror attack occurred laid roses at a makeshift memorial outside the bombed metro station. He offered his condolences to the victims and said he has been in contact with the security services about the investigation.
Talking to the mediapersons, Putin said, "Reasons for the explosion are unknown, so it's too early to talk about it. The investigation will show what happened. Naturally, we always consider all options - both domestic and criminal, primarily incidents of a terrorist nature."
United States President Donald Trump called Putin after the attack on April 3, expressing his sympathies for Russians in the wake of the terror attack. The White House in a statement said President Trump offered US government's full support.
Russia's Investigative Committee said investigators have seized items relevant for investigation. The witnesses and metro employees have been questioned. Since Russia has been involved in Syria and Chechnya, it faces threats from Chechen groups and ISIS.
While the investigations are underway, let's take a look at the past terror attacks, which targetted Russia's transport system.
On December 29, 2013, a suicide bombing at a railway station in Volgograd had killed at least 16 people, including one police officer. Next day, a suicide bombing on a trolley bus killed 14 people in the same city.
On March 29, 2010, two Chechen women suicide bombers carried out two suicide attack at Moscow Metro stations, Lubyanka and Park Kultury, during the morning rush hour. At least 40 people were killed, and over 100 others were injured.
Given the history of terrorist attacks in Russia, it is difficult to infer which group is behind the latest St Peterburg bomb explosion till the investigations conclude.