The United Nations said medical evacuations from eastern Aleppo had not begun today as it had hoped, as a lack of security guarantees and agreement with all sides prevented aid workers taking advantage of a pause in the bombing announced by Russia.
The UN wants to use the four-day pause to evacuate hundreds of sick and wounded from the besieged part of the city and to make food and aid deliveries, UN humanitarian spokesman Jens Laerke told a regular UN briefing.
"It is an astronomically difficult operation whereby we need the security assurances from all sides to be there and to be adhered to, plus facilitation from all parties," he said.
He declined to give details of the hold-up but he said the UN remained optimistic and was trying hard to unblock access.
"It's not even day-by-day, it's hour-by-hour," he said.
Syria's ambassador in Geneva Hussam Aala said the Syrian government had given the UN the green light for medical evacuations two days ago.
"We have taken all measures, we have buses and ambulances ready. Unfortunately the UN is not ready to cooperate. The ball is not in our court," he told Reuters.
"It is not happening because the terrorists inside Aleppo are preventing evacuation by using mortars and snipers to attack humanitarian corridors and crossing points."
He added that the UN was making an "artificial linkage" to avoid carrying out the evacuation.
"They are quoting the demands of terrorists inside Aleppo to justify their failure to evacuate," he said. "The evacuation of wounded should be done unconditionally."
Russia has told the UN it plans to halt bombing for 11 hours per day daily until Sunday, and the UN has asked for the period to be extended. Aid rations will run out by the end of this month, and fuel and medicine are also critically low, the UN has said.
UN spokesman Laerke said the UN was ready to do four days of evacuations and to bring supplies of food and aid to the besieged citizens on the third and fourth day.
But with eastern Aleppo already well into the second day of the pause, it was unclear if sufficient time remained for the planned convoys to go by Sunday.