The horrifying decapitation of a kidnapped boy on spy accusations was “an individual” mistake, declared the U.S.-backed, so-called “moderate” Syrian rebel group that carried out the appalling crime, claiming that it will open an investigation into the beheading.

Members of the Nour al-Din Zenky Movement killed the boy, accusing him of being from the Liwa al-Quds (Jerusalem Brigade), a Palestinian militia that fights on behalf of Syrian dictator Bashar al-Assad.

Various activists on social media have identified the victim as Abdullah Issa, a 12-year-old Palestinian, notes BBC.

Other news outlets report that the boy could be as young as 10.

In a statement on Facebook, the al-Quds group reportedly confirmed it found the child was a 12-year-old Palestinian named Abdullah Issa, who lived in the rebel-controlled Mashhad neighborhood in Aleppo, Syria, with his “poor” family.

Al-Quds has denied being affiliated with the boy and suggested he was not a fighter, notes BBC.

However, his alleged sister, identified as Zoze Aisa, claimed on Facebook that the child was a pro-Assad fighter from Syria, adds the British news outlet.

“It is not clear who the boy was or why he was beheaded on camera,” acknowledges the Associated Press (AP).

Nevertheless, gruesome video footage has emerged on social media, showing the boy being taunted and then beheaded by the anti-Assad Syrian rebels who grab him by the hair as they accuse him of being a member of Liwa al-Quds.

WARNING: EXTREMELY GRAPHIC CONTENT

The video shows one of the men taking a knife to the child’s neck and decapitating him.

BBC reports that the child’s alleged sister, in a Facebook post, indicated she was angry and upset that her brother was being identified as a Palestinian.

He was a “son of al-Assad” from Homs “who went to fight rather than stay behind and receive his medical treatment,” reportedly said the sister.

Also via Facebook, the rebel group behind the horrific decapitation, Nour al-Din Zenky Movement, referred to the killing as an “individual mistake,” adding that it would investigate “the human rights abuses that were shared on social media sites,” reports CNN.

The group, which has received military support from the United States, is engaged in a bloody war against armed groups loyal to Assad and the Islamic State (ISIS/ISIL).

In the statement, it described the beheading as “individual errors that represent neither our typical practices nor our general policies,” notes CNN.

“All individuals who undertook the violation have been detained and turned over to the [judicial] committee for investigations in accordance with the relevant legal standards,” also mentioned the group, according to BBC.

The Obama administration has described the beheading as “appalling,” saying it was seeking additional information because it could not confirm what took place.

“If we can prove that this was indeed what happened and this group was involved… it would give us pause about any assistance or, frankly, any further involvement with this group,” Mark Toner, a State Department spokesman, told reporters.

The pro-Assad group, to which the boy was accused of belonging, suggested the Syrian rebels killed the child simply because he was Palestinian, in order to take “cheap and despicable revenge” for losses in battle.

AP notes:

Lebanon’s Hezbollah group, whose fighters are in Syria fighting alongside President Bashar Assad’s forces against the rebels, also pounced on the beheading.

In a statement issued in Beirut, it described the beheading as a “disgusting crime” by “so-called moderate rebels backed by the U.S. and Saudi Arabia.”