Jihadi John, Islamic State Group, Feb. 26, 2015
The Islamic State group reportedly released a video Sunday depicting the execution of five Britons. Above, a black-clad, masked member of the militant group aka either ISIL or ISIS with the alias Jihadi John stands beside a man purported to be the subsequently slain American-Israeli journalist Steven Sotloff in this still image in a video obtained by Reuters through the SITE Intel Group website Feb. 26, 2015. Reuters/SITE Intel Group via Reuters TV

A video reportedly released Sunday by the Islamic State group shows the execution of five prisoners identified as British spies. Narrated by a masked gunman speaking British-accented English, the 10-minute clip came as an explicit challenge to U.K. Prime Minister David Cameron.

“This is a message to David Cameron,” the man says in the video. “How strange it is that a leader of a small island threatens us with a handful of planes,” he says, mocking British military efforts to hobble the militant group’s advances in Iraq and Syria.

In the video, five men are depicted kneeling in orange jumpsuits before masked gunmen. After being accused of spying for Britain, they each deliver a confession in Arabic. They report hailing from Syria and Libya. At the end of the video, each is shot in the head.

The main speaker recalls the fighter dubbed Jihadi John, a British Arab who appeared in earlier clips released by the militant group aka either ISIL or ISIS, such as the video that depicted the beheading of American journalist James Foley. U.S. officials reported killing Jihadi John, whose real name was Mohammed Emwazi, in a November drone strike.

A young English-speaking boy also appears in the video, making reference to killing nonbelievers.