Reuters reports: 

At least 31 people were killed and more than 100 injured on Monday in a suicide bombing at Russia's biggest airport, Russian news agencies reported. [...] Moscow suffered its worst attack in six years in March 2010 when two female suicide bombers from Russia's volatile Dagestan region set off explosives in the metro, killing 40 people. The Kremlin is struggling to contain an Islamist insurgency in the mainly Muslim North Caucasus, and rebels have repeatedly vowed they will take their battle to the Russian heartland.