Footage shows Syrian rebels beheading boy in Aleppo

A video circulating on social media on Tuesday depicted rebel fighters beheading a boy after capturing him north of Syria's second city Aleppo, a monitor said.

The video showed the boy lying down in the back of a truck as a fighter begins to cut off his head with a small knife.

One fighter shouts "We will leave no one in Handarat!", an area north of Aleppo city, where there has been fighting between rebels and government forces.

The Britain-based Syrian Observatory for Human Rights confirmed that the video depicted rebel fighters.

In an earlier clip, the boy was sitting in the back of the truck with fighters around him accusing him with being a member of al-Quds Brigade, a Palestinian group fighting with the government forces.

Earlier in July, Amnesty International issued a report saying that some rebel fighters in Syria were guilty of war crimes, accusing them of "a chilling wave of abductions, torture and summary killings".

The London-based rights group named five Syrian anti-government factions operating in northern Syria including Nureddin Zinki.

Activists accused Nurredin Zinki of carrying out the killing, but the group issued a statement condemning a "violation" that was "an individual mistake, that does not represent the general policy of the group".

Nurredin Zinki is among rebel groups which are reported to have received financial and military support from countries including Turkey, Qatar and other Gulf states, according to the Amnesty report.

The group is also reported to have received support from a coordination body known as the northern operation command (better known by its Turkish acronym MOM), which was established by the US and allies including France, Qatar, Saudi Arabia, Turkey, the United Arab Emirates and the United Kingdom in 2014, according to Amnesty.

But funding to Nurredin Zinki was reportedly stopped in September 2015 after it joined forces with two groups accused of kidnapping two Italian humanitarian workers.

Addressing a press briefing on Tuesday, US State Department Mark Toner appeared unclear as to whether Nurredin Zinki was among rebel groups currently benefiting from American support.

"We understand from unconfirmed reports that the group, the Free Syrian Army, has appointed a commission to investigate the incident and that they’ve made arrests of those allegedly involved," Toner said.

He added that if allegations of the beheading proved true, it would give the US "serious pause" to "look at any affiliation or cooperation with this group we may have going forward".

According to Rami Abdel Rahman, Syrian Observatory for Human Rights chief, "the boy is no more than 13 years old, he was captured Tuesday in Handarat area, but the incident took place in a rebel-held area in Aleppo city, al-Mashhad neighbourhood to be exact."

He could not confirm if the boy was a Palestinian or a child soldier, though he said al-Quds Brigade denied that he was one of its fighters.

Nureddin Zinki added that "the persons who carried out this violation were arrested and handed over" to a judicial committee for investigation.

Syria's conflict began in 2011 with the repression of anti-government demonstrations and has evolved into a multi-front war that has left more than 280,000 dead and forced millions from their homes.