The Syrian Observatory for Human Rights said the Sunni tribesmen were from Shaitat, near Deir ez Zor, which has long been considered a key strategic target for the Islamic State owing to the eastern province’s considerable oil revenue.

Rounded up and marched into the desert, they are made to kneel on the dusty grouind before being systematically shot in the head.

Others aren’t so lucky. One image shows a jihadist fighter gleefully carving off a prisoner’s head as the victim screams in agony.