U.S.-backed Syrian rebels, screaming "Allahu akbar," allegedly beheaded a child named Mahmoud Issa on Tuesday, according to the Associated Press.
The group, known as Nour el-Din al-Zinki, is a moderate faction that has been fighting the Syrian government and the Islamic State group and has received support from the United States in the past.
The group called the incident an "individual mistake," saying that it does not represent the group as a whole. The group went on to condemn the beheading incident which was captured on video and immediately triggered an instant backlash against them.
It is not clear who the boy was or why exactly he was beheaded on camera. According to the Associated Press, he was a 12 year-old Palestinian. The Syrian government has said the boy was from the Palestinian refugee camp of Handarat on the outskirts of Aleppo.
The killing occurred in Handarat. The boy was seen on the back of a pickup truck surrounded by armed men (from the Nour el-Din al-Zinki group), who accused him of being a spy and a member of the Quds Brigade, a pro-government Palestinian militia. He was then beheaded with a knife by one of the group members.
The Quds Brigade group itself claims that the boy was killed by a "terrorist" member of Nour el-Din al-Zinki as revenge for his brother, who was killed in fighting with the Quds Brigade near Handarat.
U.S. Secretary of State John Kerry told the Associated Press he had seen the "appalling report," but could not confirm it happened.
"Obviously we're very concerned certainly if it's accurate," he said, adding that if the report is proven, it would "give us pause about any assistance or, frankly, any further involvement with this group."