Russia has vetoed a UN resolution to end the bombing of Aleppo.
Another resolution also failed.
The UN is warning that if air strikes continue on rebel-held areas, Syria's second largest city will be destroyed by the end of the year.
UN chief Ban Ki-moon says Aleppo is "worse than a slaughterhouse".
The UN says two million Syrians could be trapped in the city.
More than 400 civilians, about one-third of them children, have been killed during the past two weeks of bombardment.
Only five hospitals remain operational in the besieged part of eastern Aleppo.
Who is really calling the shots in this complex conflict?
Presenter: Adrian Finighan
Meguerditch Terzian - President, Doctors Without Borders
Sergey Markov - Spokesman for President Vladimir Putin and Director of the Institute for Political Studies
Hillary Mann Leverett - Former White House National Security Official
Monzer Akbik - Spokesman for Syrian opposition group Tomorrow Movement
Source: Al Jazeera