Hundreds of civilians are queuing up with small bundles of their personal belongings, in anticipation of being evacuated from the neighbourhood of Marjeh in Aleppo.
Russian Foreign Minister Sergei Lavrov says it is the largest operation of its kind so far.
More than three quarters of the rebel-held areas of Aleppo have now fallen under the government’s control.
This includes the symbolically-important neighbourhood of ancient Aleppo.
The UN thinks around 100,000 people remain in eastern Aleppo.
Allegations against the opposition forces
There are claims rebel fighters tried to stop people from leaving:
“We were on the ground floor of our building, when we saw the army we tried to get out but the rebels would not let us out,” one young boy told reporters.
“They asked, do you want to join the army and kill us?”, his brother added.
“The rebels told us, “the army will kill you.”
“Hundreds of men are missing” – UN
Hundreds of men from eastern Aleppo have reportedly gone missing after leaving rebel-held areas of the city and entering government territory.
The UN’s human rights office is “deeply concerned” about their fate.
How did the news get out?
The UN’s human rights spokesman Rupert Colville told reporters at a news briefing in Geneva that there have been “worrying allegations that hundreds of men have gone missing after crossing into government-controlled areas” of Aleppo.
“Given the terrible record of arbitrary detention, torture and disappearances, we are, of course, deeply concerned,” he said.
“During the last two weeks, Fatah al-Sham Front, formerly known as the al-Nusra Front, and the Abu Amara Battalion, are alleged to have abducted and killed an unknown number of civilians who requested the armed groups to leave their neighbourhoods in order to spare the lives of civilians.”
“The groups have reportedly demanded that activists inform them of civilians attempting to leave, along with the names of those who participated in protests against the presence of Fatah al-Sham Front and groups affiliated with them in the al-Ferdous and Bustan al-Qasr neighbourhoods a few weeks earlier.”
“We have also received reports that between 30th of November and 1st of December, armed opposition groups fired on civilians attempting to leave the Bustan al-Qasr area towards government-controlled Masharqa.”
A “potential war crime”?
Around 100,000 civilians are thought to remain in the “ever-shrinking” opposition-held areas of the country, Colville added.
Citing the reports that rebels had prevented some civilians from fleeing to safety, he said this would be considered as a potential war crime.