GENEVA - The senior advisor to the UN special envoy for Syria said Thursday that the UN is prepared to monitor and assist evacuations from the last rebel-held enclave in Syria's city of Aleppo.

"We do hope that today we start the last and successful attempt of the evacuations of the troubled city," Jan Egeland told press here after a weekly humanitarian taskforce meeting.

"We will do as much as we can to be close to and with and for those who are evacuated," he added.

According to the diplomat, a three-pronged approach is expected to see the medical evacuation of wounded and sick as well as the evacuation of vulnerable civilians and opposition fighters take place.

While invited to monitor operations, the UN was not part of the agreement, the fruit of direct negotiations between parties to the conflict.

According to Egeland, most evacuees are expected to go to opposition-controlled Idlib. An undetermined number may also end up in neighbouring Turkey.

"We stand ready to accompany those who are being evacuated not only from east Aleppo but all the way to Idlib... that will be the destination of most of the people evacuated," he explained.

Once Syria's commercial hub, Aleppo has been divided roughly in two since 2012, with western parts under government control and eastern districts held by rebels.