Russia says it has no information as yet confirming that two men who appear to be executed in a video released by Islamic State (IS) militants were Russian citizens.
The Internet video purportedly shows a young boy shooting two men who are said to be spies for Russia.
It shows the men saying in Russian that they infiltrated the Islamist militant group in Syria on behalf of Russia's Federal Security Service (FSB).
One says he is from Kazakhstan.
The Russian Embassy in Syria "is looking into the information suggesting that this could have been an execution of Russian citizens, particularly members of the Russian special services," embassy spokesman Oleg Samochkin told the Interfax news agency.
"So far, we do not have information to confirm that any of those shown is a Russian citizen," he said.
The FSB has declined to comment on the video.
With reporting by Interfax, AFP and Gazeta.ru