A Syrian opposition group says 65 people have been found shot dead in Aleppo - in what it calls a "new massacre".
The Britain-based Syrian Observatory for Human Rights said the men were found with their hands bound, and that the death toll could reach 80.
Photos posted online by opposition activists showed the muddied bodies of several men lying by a small river near the western outskirts of the city in northern Syria.
Close-up shots of some of the corpses showed they had what appeared to be gunshot wounds to the head.
Most have their hands tied behind their backs. It is not clear who carried out the killings and restrictions on independent media in Syria make it difficult to verify reports from activists.
The fighting has claimed at least 60,000 lives since it began almost two years ago. More than 700,000 people have fled the violence, according to the United Nations.
Human rights groups have accused both government forces and the rebels of carrying out summary executions.
Aleppo, the country's most populous city, has seen fierce fighting since the summer. The rival forces are stuck in a stalemate, with the city divided roughly in half between the two.
Both sides blamed the other for the killings.
An officer with the Free Syrian Army, the rebel force, told the AFP news agency that at least 68 bodies, including some of teenagers, had been recovered and that many more were still being dragged from the water.
He said they had all been "executed by the regime".
A senior government security source told AFP that many of the victims had been reported kidnapped earlier.
The source accused "terrorists" - the term usually used by the government to refer to the rebels - of carrying out the executions and spreading propaganda to deflect responsibility.
In the video, a cameraman is walking along a river filming more than 50 bodies lying on a concrete path, blood seeping from their heads.
Some of the men were dressed in jeans, shirts and trainers.