Evidence of atrocities committed by British fighters with extreme Islamist groups emerged as another round of peace talks between the regime and the mainstream opposition opened in Geneva yesterday (Monday).
The two sides spent the day arguing about the agenda, and no progress has been made. The United Nations hopes to broker another ceasefire in the city of Homs to allow the delivery of aid and the evacuation of civilians from areas besieged by government forces.
Hundreds of British citizens have travelled to Syria to fight against President Bashar al-Assad's regime. Many are believed to have joined Islamist rebel groups linked to al-Qaeda, notably Jabhat al-Nusra.
One man from London posted a video on Facebook showing a prisoner being flogged with an iron bar. The victim is apparently from the Free Syrian Army (FSA), a rival rebel movement. He is assaulted with such force that the bar breaks in half. The prisoner endures this while lashed to a car tyre.
The accompanying message on Facebook posted by the British man reads: "This FSA scum never thought we wud [sic] jump out at them and pick them up after saying some abusive words to our brothers."
He added: "Two then got ahead of themselves and swore at Allah, at this point there was no stopping us LOL although we where [sic] told to jus [sic] leave them."
This particular Facebook account has been verified as belonging to a British fighter from London.
Shiraz Maher, a senior fellow at the International Centre for the Study of Radicalisation at King's College London, said there was no doubt about its authenticity, but he was unable to name the individual involved. "When I contact them, they'll talk about the situation on the ground in Syria, but they won't give anything like biographical details," said Mr Maher.
Another man, who is also from London, tweeted a photograph showing three blindfolded prisoners with their hands tied behind their backs. "Got these criminals today. Insha'Allah they will be killed tomorrow. can't wait for that feeling when you just killed someone", reads the accompanying tweet.
Some days later, the same man posted a photograph of a bloodied hand on Facebook. "My first time!" reads the caption. This image has been picked up by numerous social media pages used by radical Islamists. Mr Maher said there was no doubt this Twitter account belonged to a British fighter from London.