Police suspect alleged suicide bombers from Dagestan militant group -- state news agency . Two brothers , suspected accomplices , have been arrested , report released . Russia has been trying to address security concerns before the Winter Olympics . A bitter battle for an independent Chechnya , lasting almost two decades , spawned an insurgency that has spilled into neighboring republics in the North Caucasus region , including Dagestan . Security concerns have been heightened since the bombings last month .
Police suspect alleged suicide bombers from Dagestan militant group -- state news agency . Two brothers , suspected accomplices , have been arrested , report released . Russia has been trying to address security concerns before the Winter Olympics . Security concerns have been heightened since the bombings last month .