The Islamic State released a video Wednesday in which a Russian-speaking man confesses to spying for Russia's security service and then is shown apparently being beheaded by another Russian-speaking man.
The authenticity of the video or the claims in it could not immediately be confirmed, and there was no comment from Russia's Foreign Ministry or its FSB security service.
The prisoner, appearing to be in his late 20s, is shown speaking from a chair. He says he is from Chechnya and was pressured into working for the FSB, to report on Russians who had gone to fight with ISIS.
The video then shows the man kneeling on a bench while another man stands behind him, declaring that Russians will be killed in retaliation for Russian airstrikes against ISIS. The man then places a large knife against the prisoner's throat and appears to begin decapitating him.
ISIS has beheaded a number of captives and posted videos online since August 2014 - among them U.S. journalists Steven Sotloff and James Foley, U.S. aid worker Abdul-Rahman Kassig, British aid workers David Haines and Alan Henning, and Japanese journalist Kenji Goto.
Last month, the U.S. military said it was "reasonably certain" a drone strike in Syria killed "Jihadi John," who appeared in several videos depicting the beheadings.
U.S. and coalition forces have stepped up attacks on ISIS since the Paris terror strikes last month.
On Wednesday, the coalition pounded ISIS targets near the extremist-held Iraqi city of Ramadi. Iraqi forces have encircled Ramadi and this week asked the city's civilian residents to leave - a sign that a major operation could be imminent.
The coalition said its aircraft conducted 15 airstrikes in Iraq on Wednesday, nine on ISIS targets near Ramadi, including fighting positions, vehicles, weapons, and buildings. Also hit were ISIS units and vehicles in Iraq's north, outside the recently liberated town of Sinjar.
In Baghdad, a coalition spokesman, Col. Steve Warren, said the strikes were in support of Iraqi operations to liberate Ramadi.