Rows of men allegedly executed have appeared in videos uploaded to the Internet by activists opposed to Syrian President Bashar al-Assad.
The footage shows dozens of men, purportedly found dead in the northern city of Aleppo with gunshot wounds to their heads.
The Syrian Observatory for Human Rights, a British-based NGO which aims to provide information on casualties from both sides of the conflict, says the death toll here could be as high as 80.
One activist, recorded in another video, said “these men were killed only because they were Muslims”.
It is impossible to verify such footage from Syria because of tight media restrictions in the country.
Meanwhile, refugees are flooding into neighbouring countries. According to the United Nations, some 700,000 people have fled Syria. Within Syria, the UN says there are four million in need and it has brought food to up to 1.5 million.
But the country’s main opposition coalition has been critical, saying the UN has allowed aid distribution to be controlled by the Syrian government and organisations sympathetic to it.