The UN cited reports of regime forces executing scores of civilians in Aleppo, as the attack on the rebels enters its final stage. Activists and opposition leaders sent out increasingly desperate pleas for a truce.
The situation in Aleppo indicates "a complete meltdown of humanity," UN humanitarian spokesman Jens Laerke said on Tuesday.
At the same time, spokesman for the UN human rights' office Rupert Colville voiced "deepest foreboding" for thousands of civilians trapped in the "last hellish corner" of the city where the rebels remain in control.
"In all, as of yesterday evening, we have received reports of pro-government forces killing least 82 civilians, including 11 women and 13 children, in four different neighborhoods," Colville told reporters, adding that there could be "many more."
"We have also been informed that pro-government forces have been entering civilian homes and killing those individuals found inside," he added. Some civilians trying to flee "were reportedly caught and killed on the spot and others were arrested," he said.
Civilians could 'all be evacuated' in a day
The reports come as President Bashar al-Assad's forces fight the last remaining resistance in the once-divided city. Regime officials recently said they were just hours away from declaring victory in the weeks-long offensive.
The pro-rebel medical charity Syria Civil Defence, better known as the White Helmets, said that 100,000 civilians were still inside the narrow opposition-held area.
"We know that the UN has a plan to get us out across the 4 kilometers of Western Aleppo to safety; with a few dozen buses and lorries we could all be evacuated in 24 hours. However, we need you to guarantee the safety of their workers and our own," they said, appealing for a humanitarian truce on Monday night.
"If we stay we fear for our lives," they said. "The regime has been trying to kill us for five years. Please don't give them this chance."
Russia and Damascus have mostly ignored the calls for a break in fighting. Last week, the Kremlin announced that pro-government forces temporarily suspended their offensive in order to allow civilians to leave. However, activists reported that heavy clashes continued.
Hollande: Aleppo residents held hostage
On Tuesday, Turkey said it would intensify talks with Russia and its allies "so we can find a solution to this humanitarian tragedy," according to Foreign Minister Mevlut Cavusoglu.
"We're seeing the most cruel form of savagery in Aleppo, and the regime and its supporters are responsible for this. The wounded are not being let out and people are dying of starvation," Cavusoglu told reporters in Ankara.
"However, we will continue our efforts. Even if everyone remains silent, we will not be silenced," he added.
France has also been vocal on demanding a truce from Russia. After meeting with Germany's Angela Merkel in Berlin on Tuesday, Francois Hollande said that 120,000 people were being "held hostage" in Aleppo.
The Russians "will be responsible for a situation that they helped create if they do nothing to allow access for humanitarian aid." It was time to send "a humanitarian ultimatum," the French president added.
dj/msh (Reuters, AFP, AP, dpa)