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 .
Police says alleged suicide bombers from Dagestan militant group -- state news agency . Two brothers , suspected accomplices , have been detained , report says . Russia has been trying to address security concerns before the Winter Olympics . Security fears have been heightened since Volgograd bombings last month .