Rebels in Aleppo called for a five-day truce and the evacuation of civilians yesterday after losing more than three quarters of their territory including the Old City to a Syrian army offensive.
In the face of a blistering assault by forces loyal to President Bashar al-Assad, the rebels were reported to have retreated from all of Aleppo's Old City, the latest in a string of territorial losses.
After three weeks of heavy fighting, regime forces appeared closer than ever to retaking all of Aleppo and winning their most important victory yet in the civil war that began in 2011.
Rebel fighters have rejected calls to withdraw from the city, which had been divided between government and opposition forces since 2012, but yesterday issued a joint statement calling for an "immediate five-day humanitarian ceasefire".
The statement, which rebel representatives told AFP had been approved by all armed opposition factions in the city, called for "the evacuation of civilians who wish to leave" the city's east to rebel territory in northern Aleppo province.
It made no mention of the fate of rebel fighters and urged "negotiations on the future of the city".
Syria's government has said it will not agree to any ceasefire in Aleppo without a guarantee of a full rebel withdrawal.
The army and allied forces are now in control of 75 percent of the territory previously held by rebels in east Aleppo, the Observatory said.
The offensive showed no signs of slowing and overnight the army carried out heavy shelling of the Al-Zabdiya neighbourhood and other territory still under rebel control in the southeast of the city, the monitor said.
The assault has prompted a mass exodus of east Aleppo residents and the Observatory yesterday said that at least 80,000 had now fled their homes.
Assad's government has been urging civilians to leave east Aleppo for months and accused rebels of holding residents hostage for use as "human shields".
As they moved into new areas, Syrian soldiers were helping residents to evacuate.
Diplomatic efforts to end the fighting have stalled despite widespread international concern, with Moscow and Washington trading accusations of blame.
US Secretary of State John Kerry said Tuesday he would work for peace talks to restart. Kerry, who has had repeated meetings on Syria with his Russian counterpart Sergei Lavrov, said they would meet again on Wednesday or Thursday in Hamburg, Germany.
Russia had announced talks with the United States in Geneva this week on organising a rebel withdrawal from Aleppo ahead of a ceasefire, but then Lavrov accused Washington of backtracking.
Ankara meanwhile was working to facilitate negotiations between Moscow and Syrian opposition groups, Turkish Prime Minister Binali Yildirim told Russia's Interfax news agency.
The offensive has killed at least 369 people in east Aleppo, including 45 children, the Observatory says. Rebel fire into the west of the city has killed at least 92 people, including 34 children, it adds.