Militants linked to al-Qaeda have asked for forgiveness after they severed the head of the wrong man and displayed it in front of a crowd.
In a sickening video posted on YouTube, soldiers from the Syrian-based group Islamic State of Iraq and al-Sham (ISIS) were seen holding up the decapitated head of a soldier they believed was a supporter of President Bashar al-Assad.
But, after the footage was made public, the victim was recognised by an extremist as a fellow rebel fighter who had been wounded during a battle.
The Syrian Observatory of Human Rights said ISIS fighters misunderstood comments Mr Fares made about the founding fathers of Shia Islam, Imams Ali and Hussein, according to The Daily Telegraph.
It is thought Mr Fares was injured while fighting pro-Assad forces for the control of military site Base 80 near Aleppo, before he was mistakenly executed.
The militant group tried to explain their error by referring to a story in which the prophet Mohammed said Allah would forgive a man who killed a believer by mistake.
An ISIS spokesman, Oma al-Qahtani, confirmed Mr fares had been injured in fighting and had been captured by soldiers who believed he was fighting against them.
He has now said an investigation into the death would be carried out by the appropriate authorities.
The huge mistake has highlighted chaos within the rebel ranks in Syria, which Assad has taken advantage of in recent weeks during a push by his forces south-east of Aleppo.
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