Dressed head-to-toe in black, the child executes the man who he described as a 'client of the Iraqi army', anti-ISIS activists have said. 

It comes as a newly released ISIS video shows how its so-called 'cubs of the Caliphate' are brainwashed in the classroom before they are turned into the terror group's next generation of killers. In one scene the boys are kicked in the private parts as a recruiter 'toughens them up'.

And for the first time one of its rival terror groups, the al-Nusra Front, has released an image of its own young fighters wearing army fatigues and armed with automatic rifles.

The propaganda video begins with the man confessing - presumably under duress - for spying on on ISIS in the Iraqi town of Al-Qa'im, around 250 miles from the capital Baghdad, according to anti-ISIS activists Raqqa Is Being Slaughtered Silently.

Surrounded by green graphics reminiscent of the 1999 film The Matrix, the man says he was sent to gather 'information about the military sites where ISIS fighters exist'.

He looks visibly distressed as he admits 'remorse' for carrying out the covert operation and tells ISIS's opponents - including a United States-led coalition which is carrying out airstrikes on its territory - to abandon their attacks.

Flanked by four armed and masked terrorists, the young executioner looks completely calm as he loads his handgun, kneels next to the 'spy' and shoots him in the head. 

The fresh-faced boy with very light skin continues to shoot at the man's corpse as it lies motionless on the concrete floor. The video first appeared online in May but it is unknown when the execution was filmed.

Only five days ago, ISIS leader Abu Bakr al-Baghdadi banned his minions from sharing barbaric execution videos online.

He supposedly sent a letter to the group's media officers, telling them to stop sharing the gruesome footage because they could offend fellow Muslims who might think the videos are scary for children.

That warning came just one day after the group released a video showing a young boy beheading a Syrian soldier in the first execution of its kind.

The sickening murder is thought to have taken at the Hir Palace in the Syrian province of Homs after the soldier was captured by jihadis at the nearby Al-Bosayri army checkpoint.

The unnamed officer is believed to have been a regime leader in the ancient city of Palmyra which ISIS captured in May. 

The extremists are increasingly using young boys in their gruesome executions after brainwashing them in special schools where they are taught the group's twisted version of Islam and trained how to fight.

Its newest video from an undisclosed location, which appears to have been released earlier today, shows incredibly young boys practicing with automatic weapons.

At one point, the boys line up to be punched by a senior commander who strikes them in the chest before appearing to kick them in the private parts. 

The video also shows the youngsters sitting attentively in a classroom as an older ISIS commander dressed in white presides over them.

Another terror group which battles both ISIS and the Syrian regime in the country seems to be trying to counter Islamic State's propaganda by showing off its own deadly young recruits.

The al-Nusra front was formed in January 2012 to overthrow Syrian President Bashar al-Assad during the country's bloody civil war. 

It has since been drawn into the fight against Islamic State, who control vast areas in Syria and Iraq, both on the battlefield and on the internet where ISIS's propaganda has successfully helped it recruit thousands of foreign fighters.

By hijacking their education - and minds - from an early age, ISIS can mould these children into loyal fanatics who are willing to die defending the state, a counter-terrorism expert has previously told MailOnline. 

ISIS has reprogrammed their young and impressionable minds into those of killers by 'taking over Islamic schools as part of their entire take over of Islamic society,' according to Steve Emerson, executive director of the Investigative Project on Terrorism.

It also shows them off as 'martyrs' when young recruits perish on the battlefield or in sickening suicide attacks which they are brainwashed into believing are a 'great honour'.

'They make a big point of showing off about it too by sharing martyrdom pictures and showing videos of military training,' said Charlie Winter from the Quilliam think-tank.

'For someone who is completely committed to Islamic State ideology, a hardcore supporter of jihadism and the caliphate, killing themselves in a suicide operation is the greatest honour they can receive.

'That's why you see suicide bomber registers in territory controlled by Islamic State, where you actually have to apply for who gets to kill themselves.'

'It is abhorrent what is going on here but the people who are killing themselves are not being forced into it... They have often requested it.' 

(dailymail.co.uk)