New talks are set to start in Switzerland as the US and Russia try to broker another ceasefire in Syria.
US Secretary of State John Kerry and Russia’s Sergei Lavrov are meeting delegates from Turkey, Saudi Arabia, Iran and Qatar in the city of Lausanne.
Since the collapse of a short-lived truce in September, Syria and its ally Russia have stepped up bombardment of rebel-held eastern Aleppo.
Leading charities have called for a 72-hour ceasefire for aid deliveries.
But officials have played down any hopes of a breakthrough.
On Friday, Russian news agencies quoted Mr Kerry as saying he had no “special expectations” for the talks, while an unnamed French source told AFP: “When you see the results from the previous efforts, quite frankly I’m a bit sceptical about the next ones.”
Syria’s President Bashar al-Assad has vowed to “keep cleaning”
Aleppo of rebels and told a Russian newspaper that winning in the city would be a “springboard” to winning in the rest of the country.
“It’s going to be the springboard, as a big city, to move to another areas, to liberate another areas from the terrorists,” he said, referring to the rebels.
On Saturday, organisations including Save the Children, Oxfam, the Norwegian Refugee Council and the International Rescue Committee issued a plea “to establish a ceasefire of at least 72 hours in east Aleppo”.
“This will allow the sick and wounded to be evacuated, and for food and medical aid to enter the besieged area,” their statement continued.
There are now no safe areas left in rebel-held parts of the city, according to REACH, an organisation that contacts people there regularly in order to gather humanitarian reports. About 275,000 people live in the besieged areas, and aid organisations have not been able to get to them since the siege resumed on 4 September.
More than 370 people, including nearly 70 children, have been killed in the bombardment of eastern Aleppo, according to the UK-based Syrian Observatory for Human Rights.
The monitor said dozens of civilians including children have also died in rebel bombardment of western Aleppo, which is controlled by the Syrian government.
A war that started with an uprising against President al-Assad has now split Syria into many parts. It has been going on for over five years and it has claimed 300,000 lives.