ISIS releases video showing execution of alleged Russian spy

The Islamic State in Iraq and Syria (ISIS) on Wednesday released a video purporting to show the execution of an alleged Russian spy, according to the SITE Intelligence Group. 

ISIS claims in the video that the man joined the terrorist group but turned out to be a spy, and the video includes a message threatening Russian citizens, according to CNN
 
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Before apparently executing the man, a fighter speaking in Russian says airstrikes ordered by Russian President Vladimir Putin have "only made us more certain and more firm."
 
If confirmed as authentic, the video will be the latest in a series of grisly executions of foreign nationals by the terrorist group, which has operated from a stronghold in Syria.
 
Putin vowed to retaliate against ISIS with airstrikes in Syria after the terrorist group claimed responsibility for the downing of a Russian passenger jet over Egypt on Oct. 31, killing all 224 people on board. 
 
The U.S. and France have also worked to ramp up airstrikes in Syria after last month's terrorist attacks in Paris, though a chairman of the Joint Chiefs of Staff this week acknowledged that the U.S. has "not contained" the terror group.