The U.N. human rights office said it had reports of abuses, including that the army and allied Iraqi militiamen summarily killed at least 82 civilians in captured city districts.
“The reports we had are of people being shot in the street trying to flee and shot in their homes,” Rupert Colville, a UN spokesman, said. “There could be many more.”
The Syrian Observatory for Human Rights said there were corpses abandoned in the streets with residents too terrified by the shelling to bury them. “Real massacres” were taking place in the city, the war monitor said.
Colville described the rebel-held area as "a hellish corner" of less than a square kilometre, saying its capture was imminent.
Thousands of people are reportedly trapped in the last remaining neighbourhoods still in rebel hands, facing intense bombardment as pro-government troops advance.