A Syrian rebel official said pro-Damascus Shiite militias were obstructing the departure of people from opposition-held districts of eastern Aleppo today under a deal that will hand control of the area to the government.

Officials in the military alliance fighting in support of President Bashar al-Assad could not immediately be reached for comment. Assad has been backed by an array of Shiite militias from across the region in his campaign for Aleppo.

Sources yesterday gave different expected start times for the evacuation. Opposition officials said they had expected a first group of wounded people to leave yesterday evening.

A military official in the pro-Assad alliance had said the evacuation was due to start at 5am (11am in Malaysia).

"Iranian militias are turning people back," said Zakaria Malahifji, a Turkey-based official with an Aleppo rebel group.

The Syrian Observatory for Human Rights said no fighter or civilian had left eastern Aleppo as of 5am local time.

A Reuters witness said 20 buses were parked with their engines running on a main road out of the city, awaiting the evacuees. Another dozen were counted nearby.

Earlier, dpa reported that Eastern Aleppo's rebel fighters were due to pull out of the besieged enclave this morning, as a ceasefire went into effect, with  al-Assad looking set to declare victory in Syria's largest city.

"The agreement is for the fighters to leave," said Vitaly Churkin, Russian ambassador to the United Nations, confirming rebel reports late yesterday that they had accepted a deal brokered by Moscow and Turkey.

"The civilians, they can stay, they can go to safer places, they can take advantage of the humanitarian arrangements, which are on the ground," said Churkin, insisting civilians did not need to leave after the government reasserted its power.

Churkin then went into an emergency session of the UN Security Council, declaring that military operations had ended and "the Syrian government has established control over East Aleppo."

A Syrian government source confirmed the evacuations would take place. However, there has been no official statement from Damascus about the deal for the rebel enclave, which has collapsed under a government assault following a five-month siege.

The apparent deal comes after increasingly urgent appeals from the UN and the International Committee of the Red Cross to evacuate the sick, civilians and medical workers, as government forces closed in on the last few besieged districts still under rebel control.

According to a Turkish government source, "moderate rebels" in Aleppo would be allowed to leave the city to Idlib, a neighbouring province run by the armed opposition. It remained unclear what would happen with the more extreme fighters linked to al-Qaeda.

Civilian activists and medical workers in the city have pleaded to be allowed leave over recent days, saying they fear for their lives if they fall into the hands of government forces, who have a grim reputation for disappearances and torture.

"What we have seen the last two days is indescribable," east Aleppo activist Rami Zien said, referring to intense airstrikes and shelling.

"We are hoping the agreement about evacuation in the city and the fighters... will be implemented so we can all go safely," said Zien.

Residents admitted there was uncertainty and anxiety, as details of the deal remained murky. It was unclear if people would be able to take personal belongings if they chose to leave or what fate might await them if they stayed.

Red Cross preparing contingency plans

The Red Cross said it was preparing contingency plans to help if the warring factions requested the assistance.

"We stand ready to act as a neutral humanitarian intermediary and to assist civilians who are in need, whether they decide to leave or not," said a Red Cross official in Damascus.

A Western official with knowledge of the negotiations said that the agreement had been held up by Russian insistence that al-Qaeda-linked militants, with a group known as Fath al-Sham Front, be arrested.

Al-Qaeda is on a UN terrorism list and Russia has framed much of its involvement in the Syrian civil war as part of efforts to tackle violent extremism.

A Syrian government source said the Syrian army would likely declare the city to be under its control today or tomorrow, a major victory for the government of President Bashar al-Assad.

Aleppo, Syria's largest city before the war, was the only major city still partially controlled by the opposition. The fall of the rebel-held eastern sector will bolster al-Assad's claim to be the only viable ruler of the country.

The victory would be costly for residents of the ancient city. Historic landmarks have been damaged, along with entire blocks of residential buildings.

The human price paid has been staggering. The Syrian Observatory for Human Rights reported that nearly 600 civilians were killed in Aleppo since the government began a land offensive to recapture the eastern district last month. The UN reported on massacres.

In the rebel-held eastern areas, 463 civilians - among them 62 children - were killed as a result of intensive airstrikes and artillery shelling. In the government-run sector, some 130 civilians, including 40 children, were killed by rebel shelling.

At least 532 rebel fighters also died, while 256 soldiers and militia members fighting for the government also died in the conflict.

Hundreds of thousands of Syrians have died in the civil war, which started as protests against the rule of al-Assad and his family.

- Agencies