An Islamic militant group in Russia's North Caucasus claimed responsibility for twin suicide bombings in the southern city of Volgograd last month and posted a video threatening to strike the 2014 Winter Olympics in Sochi.
There had been no previous claim of responsibility for the bombings, which killed 34 people and heightened security fears before next month's Winter Games.
In the video, two Russian-speaking men warned President Vladimir Putin that "If you hold these Olympics, we will give you a present for the innocent Muslim blood being spilled all around the world: In Afghanistan, in Somalia, in Syria."
They added that "for the tourists who come, there will be a present, too."
In a statement posted with the video on its website, the militant group Vilayat Dagestan claimed responsibility for the Volgograd bombings.