If the explosion on a subway train in St. Petersburg turns out to have been a terrorist attack, it would be the latest in a long line of attacks targeting Russia in recent years. Some of the deadliest include the following:
— October 2015: Militants from local affiliate of Islamic State down a Russian airliner en route from Sharm el-Sheikh to St. Petersburg over Egypt, killing all 224 people on board.
— October 2014: Suicide bomber wearing a police uniform blows himself up in Grozny, the capital of Chechnya, killing five policemen and wounding 12 others.
— December 2013: Back-to-back suicide bombings in the southern Russian city of Volgograd kill 34 and injure 100 others.
— January 2011: Suicide bomber blows himself up at Domodedovo Airport, Moscow's busiest, killing 35 and injuring 180 people.
— March 2010: Two suicide bombers attack Moscow subway system, setting off their explosives about 30 minutes apart on two trains during rush hour, killing at least 40 and injuring more than 100.
— November 2009: A bomb explodes under the high-speed Nevsky Express train travelling between Moscow and St. Petersburg, causing a derailment that kills 28 and injures nearly 100. A previous attempt on the rail line in 2007 caused more than two dozen injuries but no deaths.
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— October 2005: Islamic militants launch a series of attacks on police in Nalchik, capital of the tense Kabardino-Balkariya republic near Chechnya. Chechen rebels claim credit for the attack, in which 139 people were killed, including 94 militants.
— September 2004: About 30 Chechen militants seize a school in the southern town of Beslan and take hundreds of hostages — a siege that ended in a bloodbath two days later. More than 330 people, about half of them children, are killed.
— August 2004: A suicide bomber blows herself up outside a Moscow subway station, killing 10 people.
— August 2004: Two female suicide bombers bring down two Russian airliners that took off from Moscow's Domodedovo airport, killing 90 people. Chechen rebels claim responsibility for the attacks.
— February 2004: A suicide bomber strikes a subway car in Moscow during rush hour, killing 41 people and injuring more than 100.
— December 2003: A suicide bombing on commuter train in southern Russia kills 44 people, two days before Russian parliamentary elections.
— October, 2002: Chechen militants take 800 people hostage at a Moscow theater. Two days later, Russian special forces storm building and 129 hostages and 41 Chechen fighters are killed, mostly from effects of narcotic gas Russian forces use to subdue the attackers.
— August 1999: Four apartment building bombings kill about 300 people in Moscow and two other Russian cities. The Kremlin names the attacks as a key reason for sending troops back into Chechnya the following month.