|Rebels in Aleppo (AFP)|
Video posted online Tuesday shows the men, who included the alleged head of a feared local militia, being put up against a wall and shot with Kalashnikovs.
Clive Baldwin, a senior legal adviser for Human Rights Watch (HRW), told the BBC: "What it looks like is execution of detainees and if that is the case, that would be a war crime."
In turn, the UK-based Syrian Observatory for Human Rights, which documents violence by all sides in the conflict, condemned the killings by the rebels as "criminal".
Rami Abdel Rahman, head of the UK-based Observatory, said of the footage: "This is criminal. This is revenge."
Press reports indicated that shootings seem to have taken place on Tuesday, in what looks like a schoolyard.
After the half-naked men are put up against a wall, the camera moves back behind the crowd, losing sight of them.
Heavy gunfire from Kalashnikov assault rifles erupts, after which the camera shows a pile of bodies by the wall.
One of the men killed has been identified as Ali Zeineddin al-Berri, known as Zeno, accusing of leading a Shabiha group which killed 15 FSA fighters during a truce in Aleppo on Tuesday.
The Aleppo video clearly shows that large numbers of rebel fighters retain control of several parts of Aleppo and seem even to be expanding, despite reports on the state media that security forces are prevailing, says the BBC's report.
Syrian Government forces have been battling to oust Free Syria Army (FSA) rebels from Aleppo, the country's second and biggest city, since they launched an assault last month.
For its part, Amnesty International says on Wednesday that government forces committed crimes against humanity this month in Aleppo.
In the report, based on research carried out in May, the rights group appealed to the UN Security Council to refer Syria to the International Criminal Court and impose an arms embargo on the country.
Amnesty has also accused security forces and the Shabiha of firing on peaceful protesters and bystanders, including children.
Amnesty also added that medical teams were targeted and those arrested were often tortured.
Human rights activists estimate some 20,000 people have died in Syria since March last year.
The views expressed in this article are the sole responsibility of the author and do not necessarily reflect those of this Blog!