By Amie Ferris-Rotman

MOSCOW

 (Reuters) - 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.

 Russia's ruble-dominated stock market MICEX fell by nearly two percent following the blast, which ripped through the baggage claim area at Moscow's Domodedovo airport at 1332 GMT.

Smoke wafted out of the baggage claim area and people were seen running out of the emergency exits at the airport, local media reported.

Initial casualty figures were contradictory with ITAR-TASS saying about 20 people had been killed. A spokeswoman for prosecutors put the number of casualties at about 20.

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.

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(Writing by Amie Ferris-Rotman, editing by Guy Faulconbridge, Steve Gutterman and Mark Heinrich)