Syrian rebels have been accused of possibly committing a war crime after a video allegedly showing an execution of government soldiers appeared online.
The UN and Amnesty International condemned the alleged killings which reportedly took place after the rebels seized army checkpoints on Thursday.
Footage apparently shows the rebels beating soldiers before shooting them.
Unconfirmed reports say troops have now quit all bases near the strategic northern town of Saraqeb.
The town lies near both the main Damascus-Aleppo highway and the highway linking Aleppo to the coastal city of Latakia – making it doubly strategic.
The army, meanwhile, continued its air strikes across Syria on Thursday.
In all, more than 150 people reportedly died in fighting, said the Syrian Observatory for Human Rights (SOHR), a UK-based activist group.
The SOHR said that among the victims were more than 70 government soldiers, 43 civilians and 38 rebels.
The claim has not been independently verified.
In a separate development, Russian Foreign Minister Sergei Lavrov, international peace envoy Lakhdar Brahimi and Arab League Secretary General Nabil el-Araby would meet in Cairo on Sunday to discuss the Syrian crisis, the Arab League announced.
The alleged executions took place after the rebels overran the strategic army checkpoints between on Thursday.
The video purportedly shows agitated rebels kicking and pushing the soldiers to the ground inside one of the seized buildings. Shots are then seen fired into the cowering mass of bodies.
A spokesman for the UN High Commissioner for Human Rights, Navi Pillay, said: “It seems very likely that this is a war crime, another one.”
Spokesman Rupert Colville added that the video – if proved to be genuine – “will form part of the UN’s investigation into violations in Syria – an investigation which is now almost certain to end up before the International Criminal Court”.
Meanwhile, Amnesty said in a statement: “This shocking footage depicts a potential war crime in progress, and demonstrates an utter disregard for international humanitarian law by the armed group in question.”
No group has so far admitted carrying out the alleged killings.
But it is alleged that an extremist Islamist group, the al-Nusra front, was responsible.
For months, activists have reported similar summary executions by regime forces virtually every day.
But there has been mounting evidence of similar tactics being used by some rebel groups too, although many have signed a code of practice banning such abuses, our correspondent says.
US Secretary of State Hillary Clinton earlier warned that radical Islamist fighters were trying to hijack the Syrian revolution.
The comments have drawn an angry response from some opposition leaders, who say that it is the failure of the outside world to support the uprising with practical help that has left the field open to the radicals.
The SOHR more than 36,000 people have been killed since protests against President Bashar al-Assad erupted in March 2011.
The SOHR is one of the most prominent organisations documenting and reporting incidents and casualties in the Syrian conflict. It says its reports are impartial, though its information cannot be independently verified.
