The video was posted online yesterday by a militant group in Dagestan, a predominantly Muslim republic in Russia's North Caucasus.
Two Russian-speaking men featured in the video are identified as members of Ansar al-Sunna, the name of a militant group operating in Iraq. It was unclear whether they had received funding or training from the group or only adopted its name.
There was no confirmation the men were the Volgograd suicide bombers as the video claims.