Up to 16,000 civilians have fled eastern Aleppo as opposition fighters lost control of all northern neighbourhoods , the UN said Tuesday (November 29th), describing the situation as "chilling".

UN humanitarian chief Stephen O'Brien pointed to reports from the UN's humanitarian partners on the ground indicating that "up to 16,000 people have been displaced, many into uncertain and precarious situations", AFP reported.

"The intensity of attacks on eastern Aleppo neighbourhoods over the past few days has forced thousands of civilians to flee to other parts of the city," he said.

"It is likely that thousands more will have no choice but to flee should fighting continue to spread and intensify over the coming days," he warned, voicing concern over the "deeply alarming and chilling situation unfolding".

O'Brien's comments came as the Syrian regime advanced deep inside the opposition stronghold of east Aleppo, taking several neighbourhoods from the opposition in an onslaught to recapture the entire city.

The UN human rights office meanwhile voiced alarm at the dangers facing those attempting to flee the fighting.

"Adding to the dangers associated with attempting to flee across an active front-line, we have received reports that opposition groups are preventing civilians from leaving areas under their control," said spokeswoman Ravina Shamdasani.

She also voiced concern that civilians believed to have links to armed opposition groups could be detained once they reach regime or Kurdish-controlled areas.

O'Brien said the UN and its partners were trying to help those displaced by the fighting across the city, and stood ready to bring aid into eastern Aleppo and to carry out medical evacuations if they managed to get access.

Meanwhile, France on Tuesday called for an "immediate" UN Security Council meeting on Aleppo to tackle the "humanitarian disaster" in the Syrian city.