Hundreds of wounded civilians were stranded in rebel-held areas of Syria's Aleppo Saturday after the UN said security concerns had prevented evacuation convoys even as Russia extended a ceasefire into a third day.
The unilateral "humanitarian pause" in the Syrian army's devastating Russian-backed assault on the opposition-controlled east of the city has largely held since it began on Thursday morning.
The army has said it is an opportunity for civilians and rebel fighters who lay down their arms to leave.
But so far there have been no organised evacuation convoys and only a handful of the 250,000 civilians still living in the rebel sector have left under their own steam.
An AFP photographer in the Bustan al-Qasr neighbourhood at one of the crossings over the front line the army has set up for evacuations said it was deserted on Saturday morning.
After three months of siege by the army and nearly four weeks of relentless air strikes by Syrian and Russian warplanes, trust in government assurances of safe passage is minimal.
On Friday, the UN human rights council called for a special investigation into the violence in Aleppo in a resolution fiercely critical of Damascus.
The United Nations had hoped to use the ceasefire to evacuate seriously wounded people, and possibly deliver aid.
More than 2,000 civilians have been wounded since the army launched its offensive to drive the rebels out of the eastern districts they have held since 2012. Nearly 500 people have been killed.
But on Friday, a UN spokesman said evacuations had been delayed because of security concerns.
"Medical evacuations of sick and injured could unfortunately not begin this morning as planned because the necessary conditions were not in place," said Jens Laerke of the United Nations humanitarian office (OCHA).
- Four-day plan -
In the face of a mounting international outcry over Aleppo's plight, Moscow announced that the ceasefire, which was originally scheduled to last just eight hours, would be extended until 1600 GMT on Saturday.
But Laerke said that was not long enough and the United Nations has asked Russia to consider a further extension until Monday evening.
David Swanson, an OCHA spokesman in the Turkish city of Gaziantep, said a four-day plan had been drawn up to begin with two days of evacuations to government-held areas of Aleppo, rebel-held Idlib province to the west or over the border to Turkey.
If successful, the plan would then see aid delivered for another two days alongside continuing evacuations.
No aid has entered Aleppo since July 7 and food rations will run out by the end of October, UN chief Ban Ki-moon warned on Thursday.
The Syrian opposition has accused the world body of playing into the hands of Damascus and Moscow by focusing on evacuations rather providing relief supplies to allow residents to stay.
Moscow has accused jihadists among the rebels of forcibly preventing civilians from leaving.
It has warned that if fighters of former Al-Qaeda affiliate Fateh al-Shams Front do not leave the city, the offensive will resume.
- Fears of worse bloodshed -
Senior military official Sergei Rudskoi acknowledged that on the first day of the truce just seven civilians and eight wounded fighters had left.
He said the jihadists were "doing everything to prevent the exit of civilians and members of armed groups from east Aleppo."
"The terrorists are using the ceasefire in their interests," he said.
"We are seeing them massing around Aleppo and preparing for another breakthrough into the city's western neighbourhoods."
The Syrian Observatory for Human Rights warned that if the ceasefire broke down, there was the risk of even greater bloodshed.
"The regime and the rebels are both bolstering their forces, which raises fears of a massive military operation if the ceasefire fails," its director Rami Abdel Rahman said.
The UN human rights council called in its resolution on Friday for "a comprehensive, independent special inquiry into the events in Aleppo", and for those responsible for the most serious violations to be identified.
The resolution demanded that warring parties "in particular the Syrian authorities and their allies", allow unrestricted humanitarian access to desperate civilians and "end immediately all bombardments and military flights over Aleppo city".