Some 50,000 people are still trapped in eastern Aleppo even as the evacuation deal is in place. The United Nations special envoy for Syria Staffan de Mistura said most of them are civilians.

"Our priority right now is to give a chance to our UN colleagues who are there -- you know very well that I myself have asked to be able to go there," said Staffan De Mistura, UN special envoy for Syria.

"The government was not exactly OK with it -- but I would hope that there can be many of us on site to be able to help, to be with the people who are leaving."

De Mistura also warned that if there is no political agreement and a ceasefire, the city of Idlib -- where the evacuees are heading to -- will become the next Aleppo.

Meanwhile, French Foreign Affairs Minister Jean-Marc Ayrault also repeated his country's call for the quick deployment of UN observers and personnel.

A UN Security Council meeting requested by France is expected to take place on Friday. It will specifically examine the deployment of observers in order to ensure there are no abuses or acts of revenge, and that the civilian population is protected.