Islamist militants in Russia's North Caucasus have carried out numerous attacks since Russia first sent troops to crush the separatist uprising in Chechnya in the early 1990s.
Among the most notable attacks are:
*October 2002: Chechen militants seized a theater in Moscow, holding more than 800 people captive for three days. Nearly 130 hostages were killed after Russian forces stormed the building, pumping an incapacitating gas into the theater.
*September 2004: Chechen separatists seized a large group of hostages at a school in Beslan in the southern Russian republic of North Ossetia. More than 330 people were killed in that incident, half of them children.
*August 2004: Chechen rebels were blamed for the simultaneous bombing of two Russian airliners, killing 90 people.
*March 2005: Heavily armed Islamist militants attacked police and government buildings in the city of Nalchik, the capital of Kabardino-Balkaria republic. The raid triggered fierce gunbattles between the attackers and local authorities, killing about 140 people.