MOSCOW (AP) — Russia's counter-terrorism agency says it is studying a video posted by an Islamic militant group asserting responsibility for suicide bombings last month that killed 34 people in Volgograd and threatening to strike the Winter Olympics in Sochi.

The video was posted online Sunday 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.

The National Anti-Terrorism Committee said Monday it was studying the video and would have no immediate comment.

The increased terrorist activity has led some Russian news agencies to criticize the price tag on the games. The Russian Times reports that the high cost results from the focus on safety at the 2014 Winter Olympics.

FBI Director James Comey has said that the daunting task of security at Sochi has been of primary focus for Russians and added that the US will be assisting in the effort.