Executions of captives by the Sunni Muslim militants of the Islamic State have become grimly commonplace, but a newly surfaced video featured a horrifying twist: the use of a child executioner.

The Maryland-based SITE group, which monitors jihadist activity, posted the video online. Lasting just over 7 minutes, it appears to show the shootings of two alleged Russian spies at the hands of a young boy dressed in a black sweater with camouflage trousers.

Pale, with long straight hair and doll-like features, he appears to be about 12.

The video, titled "Uncovering an Enemy Within," purports to show confessions, with the men answering questions put to them in Russian. They give such information as their names and dates of birth - one says he was born in 1976 in the former Soviet republic of Kazakhstan - speaking calmly while starkly lighted against a white background.