Russia and Syria have told rebel forces in Aleppo to leave by Friday evening.
The Russian Defence Ministry said rebels would be allowed to leave unharmed and with their weapons via two special corridors on Friday, while six other routes would be opened for civilians, the sick and wounded.
The rebels have rejected the offer.
Previous attempts at humanitarian exit pauses have largely failed as the government and the rebels accuse each other of stopping people leaving.
In a statement, the Syrian army said it called on “all gunmen to stop hostilities and take the opportunity of the humanitarian grace to leave the city with their light weapons through the Castello road to the north or the Souq al-Khair – Masharqa towards Idlib”.
The corridors would be open between 09:00 and 19:00 local time (06:00 and 16:00 GMT) on Friday, the army said.
Russia said President Vladimir Putin had ordered the measures to “to avoid senseless victims”.
Meanwhile, Russia’s Foreign Minister, Sergei Lavrov, said his country sought “honest co-operation” and “a political process involving both the government and opposition forces”.
‘We won’t surrender’
The rebels rejected the offer. “This is completely out of the question,” Zakaria Malahifji of the Fastaqim rebel group told Reuters news agency.
“We will not give up the city of Aleppo to the Russians and we won’t surrender.”
Syrian government forces loyal to President Bashar al-Assad have besieged the eastern part of Aleppo, which is held by the rebels, in the hope of re-taking control.
Russia is supporting them with air strikes. Moscow says anti-government forces suffered heavy losses during a government offensive last month, and are now trapped in the rubble of Syria’s second city.
But Russia and Syria both say they have not bombed Aleppo for more than two weeks.
Meanwhile rebel groups have attacked western Aleppo, which is held by the government.
“The terrorists have suffered heavy losses in lives, weapons and equipment,” the Russian Defence Ministry said. “They have no chance to break out of the city.”