The US and Russia have been holding talks in Switzerland with the aim of brokering another ceasefire in Syria.
US Secretary of State John Kerry and his Russian counterpart Sergei Lavrov, met with delegates from Turkey, Iran, Saudi Arabia and Qatar in the south-western city of Lausanne to revive the short-lived truce which collapsed in September.
Syrian and Russian forces have increased attacks on rebel-held eastern Aleppo since the end of the last ceasefire.
On Saturday, humanitarian organisations including Oxfam, Save the Children, the Norwegian Refugee Council and the International Rescue Committee called for a ceasefire of at least 72 hours in eastern Aleppo.
"This will allow the sick and wounded to be evacuated, and for food and medical aid to enter the besieged area," the groups said in a statement.
At least four children were killed and at least 10 wounded on Thursday after a shelling near a school in government-held western Aleppo.
Syrian President Bashar al-Assad vowed to continue "cleaning" Aleppo of rebels, telling Russian media outlet Komsomolskaya Pravda that wresting control of Aleppo would allow the regime to "liberate" other areas of the country from "terrorists".
"We are working with the international community to look at how to bring the conflict to an end," the spokesperson said.
"We need to think through carefully the consequences of any action. We are talking to partners about if there any more we can be doing to end this appalling conflict."
On Saturday, Syrian rebels backed by Turkey began an attack on the Islamic State-held village of Dabiq in northwestern Syria.