Downing Street has insisted a murderous Islamic State video featuring a masked extremist and a young boy with British accents shows the terrorist group is "under pressure".
The footage released online appears to show the brutal killing of five men accused of spying for the UK.
A jihadi is seen waving a gun as he mocks Prime Minister David Cameron and the RAF bombing campaign against IS in Iraq and Syria.
Five men in orange jumpsuits "confess" to filming and photographing sites in exchange for money within Raqqa, the capital of IS's self-declared caliphate.
The militant claimed the Government had "abandoned these spies" as the men are seen kneeling before they are shot in the head.
Following the killings the 10-minute clip ends with a little boy dressed in military fatigues and wearing a black headband.
Speaking with what sounds like a British accent the child points into the distance and says in English: "We are going to go kill the kaffir (non-believers) over there."
IS - also known as Daesh, Isil and Isis - has used children in a number of previous propaganda videos.
The latest film, which is being studied by security services, bears similarities to those which featured the British jihadist known as Jihadi John.
The killer, real name Mohammed Emwazi, appeared in videos showing the murders of Britons David Haines and Alan Henning, plus those of US journalists James Foley and Steven Sotloff. Emwazi was killed in a US drone strike in Syria in November.
It comes days after Mr Cameron promised to crack down on IS sympathisers, stressing in a New Year's message that all Britons should have "loyalty" to their country.
The Prime Minister's spokeswoman said of the video: "He is clear it reflects the barbarity of this organisation but it is also a propaganda tool.
"This is a terrorist group we are seeing put under pressure."
The spokeswoman said British forces had carried out 11 airstrikes on IS targets in Syria since the Commons authorised action last month, including an attack on checkpoints near Raqqa on Christmas Day.
She declined to criticise media outlets for using images from the video, stressing that such decisions were for editors to take.