Syrian pro-government forces have been entering homes in eastern Aleppo and killing those inside, including women and children, BBC reported.
The UN's human rights office said it had reliable evidence that in four areas 82 civilians were shot on sight.
"We're filled with the deepest foreboding for those who remain in this last hellish corner" of eastern Aleppo, UN human rights office spokesman Rupert Colville told a news conference.
He said that of the 82 civilians reportedly shot by pro-government forces, 11 were women and 13 were children.