At least 65 people, apparently shot in the head, were found dead with their hands bound in a district of the northern Syrian city of Aleppo yesterday.
The British-based Syrian Observatory for Human Rights said the death toll could rise to 80 in what it called a new massacre.
Photogrraphs posted online by activists showed the bodies of about a dozen men lying by a river in the Bustan al Qasr neighbourhood.
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Meanwhile, more than 700,000 Syrian refugees have registered in neighbouring countries or await processing there, and aid workers are struggling to keep up with the exodus.
A UN spokeswoman said: "We have seen an unrelenting flow of refugees. We are running double shifts."