Syria conflict: Russia proposes safe corridors for Aleppo
Russia has indicated it is ready to discuss opening four safe corridors to the besieged, rebel-held east of the Syrian city of Aleppo, the UN says.
Humanitarian adviser Jan Egeland said they might be used to supply food and medicine to the 250,000 people there.
Conditions were now so dire that medical operations were being conducted without anaesthetics, he warned.
Russian-backed Syrian government forces have retaken more than a third of eastern Aleppo since the weekend.
On Thursday, state media reported that the Syrian army had captured the Sakan Shababi and Masaken al-Buthuth al-Ilmiya areas.
But the Syrian Observatory for Human Rights, a UK-based monitoring group, said clashes were continuing inside Sakan Shababi and also that rebel fighters had regained part of Sheikh Saad, in the south.
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At a news conference in Geneva, the head of the UN's humanitarian task force for Syria said Russia had announced it wanted to "sit down in Aleppo with our people there to discuss how we can use the four corridors to evacuate people".
"We have at least 400 wounded that need immediate medical evacuation," Mr Egeland said, adding that there would also be discussions about using the corridors to "get medical supplies and food in" for the first time since July.
Mr Egeland acknowledged that previous attempts to set up humanitarian corridors had not been successful due to "issues with both sides".
He said Russia had promised to respect the corridors, and that UN officials now felt confident that rebel groups would do the same.
"I think it has dawned upon all sides the urgency of the situation," he said.
Russia unilaterally declared the creation of humanitarian corridors in October to allow civilians and rebel fighters to be evacuated during a three-week pause in air strikes, but the UN was not involved and few people took up the offer to leave.
Without access to the east, UN aid agencies are strengthening their presence in government-controlled western Aleppo, the BBC's Imogen Foulkes in Geneva says.
Mr Egeland said the UN has enough food stored in the west to feed 150,000 people in the east, as well as medical supplies to cover their needs.
"It is pre-positioned, we have people there we basically need the access and we're sitting down now to discuss it with Russia and with the government of Syria."
He added that at least 27,000 people had fled the east for government- and Kurdish-controlled areas since the weekend.
They are joining 400,000 long-term displaced people already in the west of the city.
It is likely the UN also wants more of its own staff on the ground as witnesses, amid reports that those fleeing rebel-held areas are being detained, our correspondent adds.
Aleppo was once Syria's largest city and its commercial and industrial hub before the uprising against President Bashar al-Assad began in 2011.
It has been divided in roughly two for the past four years. But in the past 11 months, Syrian troops have broken the deadlock with the help of Iranian-backed militias and Russian air strikes.
In early September they reinstated a siege of the east, and launched a large-scale offensive to retake full control of the city later that month.
The Syrian Observatory says more than 300 civilians have been killed in rebel-held districts since the offensive was stepped up in mid-November. Another 48 civilians have died as a result of rebel rocket-fire on government-controlled areas, it adds.