The troops and allied militiamen have killed at least 80 people, burning alive four women and nine children, local pro-rebel media outlet Aleppo24 reported on Tuesday.
It said that 60 militants and civilians were shot in a public firing squads in the Bostan al-Qasr, Killasah and al-Firdaws districts of the devastated city.
Shahid Ayan Halab, another local news outlet, said conditions in the city were "apocalyptic" with dead bodies piling up in the streets and under the rubble of bombed out buildings.
Another pro-rebel outlet claimed that women were being raped at regime checkpoints in front of their husbands and children.
The UN backed up the reports on Tuesday saying that it had received reports that at least 82 execution-style killings of civilians, including women and children, had taken place in recent days.
UN human rights office spokesman Rupert Colville said the atrocities were committed in recent days, "most likely" in the last 48 hours, and that his office had the names of the victims.
|Activists have posted harrowing good-byes
on social media [@Linashamy]
White Helmets spokesperson, Ibrahim Abu Leith, told The New Arab on Tuesday that warplanes continue to bombard the final pockets of resistance and that rescue teams were not able to reach the dead and injured because of the intensity of the onslaught.
The spokesman for Ahrar al-Sham, one of the most powerful Islamist rebel factions, tweeted out comparing the ongoing atrocities to the 1995 Srebrenica massacre.
"#Aleppo is the new #Srebrenica of our time, blood is on the hands of everyone who watched and did nothing," he said.
Several activists in the city have posted harrowing good-byes on social media as regime forces closed in on them.
"We may not be able to send any more messages as regime forces push closer and closer and the airstrikes become more intense - if there even such a thing as that," OGN News reporter Bilal Adul Kareem said in a video tweet.
Lina Shamy said: "We are here exposed to a genocide in the besieged city of Aleppo. This may be my last video. More than 180 people have been field executed in the areas that the regime has recently taken control on by Assad gangs and the militias that support them."
The reports of the atrocities have come as Syrian troops seemed poised to recapture all of Aleppo, in what would be the biggest blow to rebels since they launched their uprising in 2011.