Ceasefire offer came after the opposition retreated from their last positions in Aleppo's Old City (File)
Rebels in Aleppo called for a five-day truce and the evacuation of civilians on Wednesday 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 Wednesday 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 on Wednesday 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 ceasefire offer came after opposition forces retreated from their last positions in Aleppo's Old City, a UNESCO World Heritage Site famed for its medieval buildings and souk.
The rebels withdrew from the Old City overnight after the army seized the neighbouring districts of Bab al-Hadid and Aqyul, the Syrian Observatory for Human Rights, a Britain-based monitoring group, said.
- 'We lived on edge' -
After seizing areas east of the Old City on Tuesday -- including the large and strategic Shaar neighbourhood -- the army and allied forces were 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 said Wednesday that at least 80,000 had now fled their homes.
It said the figure included residents who had sought refuge in the government-held west of the city and a Kurdish-controlled enclave, but not those who fled to remaining rebel territory.
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.
Inside one bus, evacuees could be seen huddling together, a baby wrapped in heavy blankets fast asleep at his mother's feet as she sat waiting for the vehicle to leave.
"The situation was very difficult," said Um Abdu, 30, as she left the Bab al-Hadid neighbourhood with her husband, five children, mother and siblings.
"We lived on edge for the last four days," she told AFP. "The gunmen were using us to protect themselves... but then the army came and we were able to leave."
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.
"We have been trying to find a way to get to the negotiating table... but Assad has never shown any willingness," Kerry said at a meeting of NATO foreign ministers in Brussels.
"Russia says Assad is ready to come to the table... and I am in favour of putting that to the test," he said.
- 'Systematic obstruction' -
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.
Moscow is a key Assad ally and launched an air war in support of his forces last year, while Washington has supported rebel forces battling the regime.
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.
Kerry denied any change of plans and Washington itself accused Moscow of stalling after Russia and China blocked a UN Security Council resolution on Monday calling for a seven-day ceasefire.
French President Francois Hollande on Wednesday denounced Russia's actions at the Security Council.
"Russia's systematic obstruction bolsters the regime of Bashar al-Assad in its destructive drive which is harming the defenceless civilian population," a statement from Hollande's office said.
Ankara meanwhile was working to facilitate negotiations between Moscow and Syrian opposition groups, Turkish Prime Minister Binali Yildirim told Russia's Interfax news agency.
"We are doing everything possible to bring about contacts between opposition representatives and Russia and have achieved very good success on this score," he said in an interview published Wednesday.
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, in the same period, it says.