Militants from Chechnya and other restive regions in Russia's volatile North Caucasus have targeted Moscow and other areas with bombings and hostage-takings, but the allegations of involvement in the Boston Marathon explosions would mark the first time they had conducted a terror attack in the West.

The conflict in Chechnya began in 1994 as a separatist war, but has quickly morphed into an Islamic insurgency whose adepts vow to carve out an independent Islamic state in the Caucasus.

Militants from Chechnya and neighboring provinces have launched a long series of terror attacks in Russia, including a 2002 hostage-taking raid in Moscow's theater, in which 129 hostages died, a 2004 hostage-taking in a school in Beslan that killed more than 330 people, and numerous bombings in Moscow and other cities.