A Syrian opposition group says 65 people, apparently shot in the head, have been found dead, with their hands bound, in Aleppo.

The Britain-based Syrian Observatory for Human Rights said the death toll could rise as high as 80, calling the killings a "new massacre".

Photos posted online by activists showed the muddied bodies of several men lying by a small river.

Close-up shots of some of the corpses showed they had what appeared to be gunshot wounds to the head.

It was not clear who carried out the killings.

The fighting, which began almost two years ago, has claimed more than 60,000 lives. Human rights groups have accused both government forces and the rebels of carrying out summary executions.