Geneva: The United States and Russia must broker an evacuation from east Aleppo, UN Syria humanitarian adviser Jan Egeland said on Thursday.
Five months of negotiations over aid plans have produced "nothing", Egeland said, and it was up to the United States and Russia to try to coordinate a deal.
"The member states that are supposed to help us get access to civilians in the crossfire are poles apart in how they regard what is happening in Syria," he told reporters after a weekly Syria humanitarian meeting led by the United States and Russia.
US Secretary of State John Kerry said after talks in Hamburg with Russian Foreign Minister Sergei Lavrov he was "hopeful" about reaching an agreement but he was awaiting "certain feedback and input".
Opposition groups in eastern Aleppo are simply asking for a pause in the fighting to allow people to leave, with no strings attached, Egeland said.
Russia wants eastern Aleppo`s citizens to leave via four humanitarian corridors, although it will not let food go in to supply the hungry population.
"Russia said they will definitely be discussing with us how to organise the evacuations, but they are not any more promising any pause (in fighting)," Egeland said.
More than 800 people have been killed and 3,000-3,500 wounded in the past 26 days, while those still trapped await an effective death sentence and needed safe passage, Aleppo`s council president Brita Haji Hassan said.
A UNICEF volunteer was shot dead in a "child-friendly space" and a mortar hit another U.N. location, with no casualties, but both sites temporarily suspended work, the UN said.
Nearly 150 sick and disabled civilians were evacuated overnight from a hospital in Aleppo`s Old City, the first major medical evacuation, the International Committee of the Red Cross said.
The UN described east Aleppo`s health situation as "catastrophic".
Some 1,500 people need medical evacuation, including 500 "seriously wounded", said Tawfik Chamaa of the Union of Syrian Medical Relief Organisations, as per Reuters.
The UN estimates about 33,000 people have been displaced in the past 10 days, including about 20,000 going into government-held areas. But Syria`s government says 30,000 have been registered in government-held zones alone.
Russia wants rebels and their families to be evacuated to the rebel-held town of Idlib, but the rebels want evacuees to go to northern Aleppo province.
Egeland said the local council in Idlib had informed the United Nations the town could not receive any more people because it was already too full of displaced people.
Syria army advances
Meanwhile, the Syrian army`s advanced in Aleppo slowed on Thursday but a victory was still firmly in sight after President Bashar al-Assad vowed that retaking the nation`s second city would change the course of the six-year civil war in his favour.
Lightning gains in recent days in which government forces and their allies recaptured Aleppo`s historic Old City lost some momentum in the face of stiff rebel resistance but the Syrian leadership was confident.
Assad has long sought to seize divided Aleppo which would put him in control of Syria`s major cities, the south, central spine and western flank bordering the Mediterranean, dealing a devastating blow to rebels who have fought to unseat him.
Outside of Aleppo, the government and its allies are also putting severe pressure on remaining rebel redoubts. Assad said in an interview with a Syrian newspaper that victory in Aleppo would be a landmark, but not the end of the war.
(With Reuters inputs)