An explosion on the Saint Petersburg metro Monday killed 10 people and left dozens more injured as Russia's Investigative Committee said it was probing an "act of terror".

Here is an overview of previous deadly attacks carried out on Russian transport since 1999:

- October 31, 2015: A bomb on a plane carrying Russian holidaymakers from Egypt explodes, killing all 224 people on board. Islamic State jihadists claim the attack, which comes one month after Moscow launched air raids in Syria to shore up Bashar al-Assad's regime.

- October 21, 2013: A suicide bomber targets a bus packed with students in Volgograd, the southwestern city formerly known as Stalingrad, killing six. The bomber was from the volatile North Caucasus region of Dagestan.

- December 29, 2013: A suicide bomber strikes at Volgograd's main train station, heightening security fears six weeks before Russia hosts the Winter Olympic Games.

The next day, another suicide bomber targets a packed trolleybus in the same city. The twin attacks kill 34 people.

President Vladimir Putin puts the army on high alert, and the Olympics take place without major incident.

- January 24, 2011: A suicide bombing kills 37 people at Moscow's Domodedovo international airport. Islamists from the Caucasus Emirate group claim responsibility.

- March 29, 2010: Forty people are killed when two female suicide bombers blow themselves up in metro stations in central Moscow. The Caucasus Emirate group again claims responsibility.

November 27, 2009: A bomb in a passenger train running from Moscow to Saint Petersburg kills 28 people. Islamists claim responsibility.

- August 24, 2004: Suicide bombers set off explosions on two planes travelling from Moscow to southern Russian cities, killing a total of 90 people.

- February 6, 2004: A bomb rips through a packed Moscow subway train during the morning rush hour, killing 41 people.

- December 5, 2003: A blast hits a train travelling from Kislovodsk to Mineralnye Vody in the Russian Caucasus, killing 46 people. The attack was claimed by Chechen warlord Shamil Basayev.

- August 8, 2000: A bomb blast kills 13 people in an underground passage near a busy metro hub in Moscow. Authorities raise two possibilities: a Chechen terrorist attack or a battle by criminal gangs for control of shops in the passage.