The United Nations has described the situation in the Syrian city of Aleppo as ‘catastrophic’.
A human rights group estimates that six days of air strikes and rebel shelling in the city have killed around 200 people, around two-thirds of them on the opposition side.
The city is split between government and opposing forces.
On Wednesday air strikes destroyed a hospital and killed dozens of people in rebel-held areas of Aleppo.
The clinic was run by Medicins Sans Frontieres and the victims, who numbered at least 27, included doctors and children.
US officials said the damage appeared to be the result of Syrian government attacks. Washington has called upon Russia to use its influence to persuade President Bashar al-Assad to halt the destruction.
The Syrian government has denied targeting the hospital.
The city is at the centre of a military escalation that is undermining peace talks in Geneva aimed at ending the five-year old war.