Doha - A video appearing to show Syrian rebels beheading a Palestinian boy who they say is a pro-government fighter, is circulating on social media. The video, posted online on Tuesday, shows a group of men in the back of a truck with the terrified boy, who could be as young as 12 years old, having his head cut off by one of the fighters. In the clip, the men accuse the captured boy of being a member of the Liwa al-Quds (Jerusalem brigade), a Palestinian armed group fighting alongside Syrian President Bashar al-Assad's government."He sent us a child today, he no longer has men!" one of the rebels says in the video, seemingly referring Assad. "We will leave no one in Handarat," they added, referring to the city north of Aleppo where heavy fighting between rebels and government forces has been taking place. The UK-based Syrian Observatory for Human Rights monitoring group said the video shows fighters from rebel factions "slaughtering a boy member from the gunmen loyal to the regime". "The boy was captured during the clashes at Handarat camp this morning," the Observatory said in a statement.‘It was an individual error’The rebel group in question has been identified as the Nour al-Din al-Zinki Movement, which appeared to publish a press release on its Twitter page on Tuesday calling the beheading an "individual error that does not represent the general policy of the movement". A report published earlier this month by human rights group Amnesty International details several "war crimes and other violations of international humanitarian law" committed by the Nour al-Din al-Zinki Movement, as well as other rebel groups, throughout the Syrian Civil War.The alleged war crimes include abductions and torture.Citing sources close to the United States "northern operation command," a coordination body allegedly responsible for providing military support to rebels, Amnesty's report says the group has in the past received military and financial aid from the US, Britain, France, Turkey and several Gulf states.The funding was apparently halted in September 2015 when the movement joined two other groups that were accused of kidnapping Italian aid workers.The Syrian conflict, which began with mostly unarmed demonstrations against Assad in March 2011, has risen to more than 280 000 people, while half the country's population have been forced from their homes, according to United Nations estimates.Staffan de Mistura, UN special envoy to Syria, estimated last month that the actual death toll could be as high as 400 000 people.