Umarov, one of the most wanted fugitives in Russia, has in an online video said that the attack was a response to "Russian crimes in the Caucasus". Speaking in Russian he warned of more such attacks.
The video appeared on the Kavkaz Tsentr website and is dated Jan 24, the day of the attack.
Appearing alone, Umarov speaks to the camera, "This special operation was carried out on my orders and, God willing, special operations like it will continue to be carried out."
He argues that worldwide Muslims are under attack and condemns "Zionist and Christian regimes led by Israel and America".
The warlord has previously claimed responsibility for the the March 2010 suicide bombings on the Moscow Metro and is believed to have ordered the November 2009 bombing of a train from Moscow to St Petersburg.
Doku Umarov is the leader of the "Caucasus Emirate", an Islamist militant group. He is one of the few prominent Chechen rebels still active.