We're bringing out live coverage of the situation on Aleppo to an end for now.
We'll continue to update our main story on topic with the latest developments as they happen.
The UN Secretary General, Ban Ki-moon, used what is probably his last press conference in the role to decry the international response - or lack thereof - to the Syrian crisis.
"The carnage in Syria remains a gaping hole in the global conscience," he said.
"Aleppo is now a synonym for hell.
"As I told the Security Council three days ago, we have collectively failed the people of Syria."
Abdul Kafi Alhamdo, an English teacher and activist in Aleppo, has tweeted about his experience earlier today when he tried to leave the city.
He said people had been waiting in "freezing" conditions since the early morning, for buses which never arrived.
"It seems that the international community decided to let us to our destiny," he tweeted.
There are still hundreds of "vulnerable" children trapped in east Aleppo, the United Nations Children's Fund (Unicef) warned.
Executive director Anthony Lake said Unicef was "extremely concerned about their fate" as he asked to be allowed to evacuate the children - some of whom are orphans - immediately.
"If these children are not evacuated urgently, they could die," he said.
More than 2,700 children have been evacuated in the last 24 hours, Mr Lake added.
France is calling for international observers to be deployed to Aleppo, and for urgent deliveries of humanitarian aid, at a meeting of the UN Security Council later today.
Its ambassador to the UN, Francois Delattre, said a draft resolution from France, Germany and other European countries could be quickly adopted if there is a consensus.
He told reporters "the immediate priority is to save lives, to stop the massacres and to avoid a new Srebrenica".
Any consensus would require Russia agreement. If one cannot be reached, Mr Delattre said France would support calling an emergency session of the UN General Assembly.
Evacuations were halted early in the day on Friday, but many people did manage to leave during the available window.
A photographer from the Getty agency was in the rebel-controlled Khan al-Aassal area, west of Aleppo city, where rebel fighters and civilians arrived.
The Syrian Civil Defence - also known as the "white helmets" - tweeted a photo it says shows civilians waiting for evacuations to resume earlier today.
The group said the stranded people have "nothing to keep them warm".
The sun set in Aleppo at about 16:20 local time (14:20 GMT).
Syrian state news is reporting an explosion near a police station in the Syrian capital of Damascus.
Reports said the blast took place in the Midan area of Damascus, though the cause is not yet clear.
Damascus lies some 300km (186 miles) south of Aleppo.
A Russian military officer has said more than 3,400 "moderate opposition fighters" laid down their arms in surrender in east Aleppo - and 350 of them are being investigated.
"During the liberation of the eastern districts of Aleppo 3,406 moderate opposition fighters have voluntarily surrendered, stopped resistance and laid down their arms; 3,056 of them were granted amnesty, and the rest are being vetted," Lt-Gen Sergei Rudskoi said.
During the briefing, carried by the Russian state news channel Rossiya 24, he also accused the US of turning a blind eye to "terrorists" in Aleppo.
"Now we have done this on our own," he said.
The stalled evacuation deal apparently hinges on evacuations of injured people from the rebel-besieged towns for Foua and Kefraya in north-western Syria. Unlike nearby rebel-held Madaya, they have received little media attention.
The Independent has just published this piece, saying a deal which allowed UN deliveries the two towns, as well as Madaya and another rebel-held town, Zabadani, broke down in October.
"Conditions in all four settlements have deteriorated since, with a lack of food, fuel and medicine as winter sets in," the newspaper reports.
But it quotes Siege Watch as saying government air drops have kept the situation in Foua and Kefraya stable.
"In the last week, Foua and Kefraya have been targeted by Islamist rockets and Madaya has been hit by Hezbollah shelling in a bloody tit-for-tat in which civilians continue to suffer," the report adds.
There are unconfirmed reports of deaths on one of the evacuation convoys, which was apparently then turned back. Opposition journalist Zouhir_AlShimale tweets:
It is unclear if this is the same incident as that reported by Turkish news agency Anadolu, which says 14 people were killed when "pro-government foreign terrorists" opened fire on a bus in a convoy.
This has not been confirmed by other news agencies.
Pro-rebel activist Lina Shamy uploaded this video from east Aleppo, blaming "Iranian militias" for breaching the ceasefire agreement.
"Very few people could leave", she says, "there are still thousands in the city, and a lot of injured".
Reports of just how many people have actually left under the evacuation programme vary from source to source.
The fate of the remaining population remains unclear.
This bus was turned back as the evacuation was halted, and is shown travelling back towards east Aleppo.
Thursday's evacuations took place mainly by bus and ambulance. But now trucks, cars and even this tractor - seen arriving in rebel-held Khan al-Assal - are also being used.
Here pro-government forces watched from a tank as the evacuation convoy turned back towards east Aleppo.
Monther Etaky, who has previously spoken to the BBC from Aleppo, describes discovering the path to the evacuation zone had been blocked when he tried to leave.
He also said internet access in Aleppo has been severely limited, in line with other earlier reports.
Syrian state television reported that buses are on their way to the two towns at the centre of today's disagreement.
The wounded, women, and children are expected to be allowed to leave the rebel-besieged villages of Foua and Kefraya in Idlib province, ending the deadlock.
A Syrian official told Reuters that evacuations from east Aleppo "will resume immediately" if the agreement is honoured in the two towns.
A rebel source told Reuters news agency that injured people will be allowed to leave two besieged towns, opening the way for new agreement on evacuations in Aleppo.
The fate of Foua and Kefraya villages, which are under siege by rebel forces, has been a stumbling block in negotiations, resulting in the suspension of evacuations today.
But now a Syrian rebel source told Retuers that Jabhat Fateh al-Sham - a rebel group formerly linked to al-Qaeda and known as the al-Nusra Front - had agreed to let injured people out of the besieged Shi'ite villages in Idlib province.
The source said the evacuation could start as early as today.
Thousands of people have been evacuated from the rebel-held parts of Aleppo since government forces re-took the areas.
Some of the evacuees are being transferred to other rebel-held areas, in a neighbouring province called Idlib. Some have gone to temporary camps, some to hospitals as far afield as Turkey, and others have found shelter with relatives, aid workers say.
But there are concerns that safety may still be a long way away - especially for those who go to Idlib.
Shortly before noon (GMT), Russia said the operation to evacuate people from rebel-held Aleppo was "complete", with only "radical and intransigent" militants left.
But that claim has been directly contradicted by a Syrian official overseeing the evacuation, who told Reuters: "The operation is not yet complete".
"There are many who should have left. But the operation halted before its end," he said.
Turkey, which brokered the deal alongside Russia, also said the evacuation process was not yet finished.
Turkish officials have said they won't be able to re-home all the evacuees from Aleppo because of potential security risks, according to a report by Reuters.
Turkey plans to take wounded people in for treatment in Turkish hospitals.
But two potential sites that have been identified for a camp, holding up to 80,000 people, would be inside Syria itself.
The Turkish Red Cross said aid groups from Turkey were setting up tents.
Dramatic video footage of children apparently fleeing sniper fire in east Aleppo has appeared on several US and UK news outlets.
The footage, recorded earlier this week by an activist and videographer in Aleppo, seems to show children flee from an evacuee ambulance under the sound of sniper fire, before taking shelter in a ruined building.
The BBC has not independently verified the footage.
You may find this video distressing.
The World Health Organization's Elizabeth Hoff, who is in Syria, has said negotiations are under way with the aim of re-starting evacuations, the Associated Press agency reports.
Ms Hoff said "there are a large number of women and children, and there are others, who are still inside and want to get out" - directly contradicting an earlier claim from Syria's allies in the Russian military.
Russia had claimed all the women and children have left the area.
It is not clear who is involved in the negotiations mentioned by Ms Hoff. Talks earlier this week broke down, with key parties saying they hadn't been consulted.
Rebels in east Aleppo told Reuters news agency that pro-government Iranian forces have detained about 25 cars full of civilians leaving the area.
They also said weaponry has been deployed on the road out.
The head of the Fastaqim group told the agency his forces were preparing for conflict.
"Everyone is manning positions and the fronts. Readiness is at the highest level", he said.
With modern technology, the world has been able to follow some residents and activists in east Aleppo throughout the crisis.
Today there are unconfirmed reports that internet access in the area has been disrupted. However, a handful of accounts are still sending messages.
The battle for Aleppo is ending and the Syrian government now controls most of a city which had put up fierce resistance for years.
But the government's victory here doesn't mean the complicated war will end.
The BBC's diplomatic correspondent, Jonathan Marcus, says this is a major propaganda victory for President Bashar al-Assad's government - following an extraordinary turnaround that happened after Russia intervened to help defeat the rebels.
But the war will continue, he says, and will "lose none of its complexity".
Russian officials say Syrian government forces have retaken every district in Aleppo, and are in the process of clearing the last remaining pockets.
"The Syrian army's operation to liberate rebel-controlled eastern Aleppo neighbourhoods is complete," the defence ministry said in a statement.
Despite this, Reuters news agency reports that buses which had begun evacuation journeys out are now turning back towards the rebel-held areas.
It is not clear how much of the city the rebels still control.
The UN estimates roughly 10,000 of the 50,000 people still living in rebel-held areas have been fighting against the government.
Elizabeth Hoff from the World Health Organization said this morning that there were "still large numbers of women and infants - children under five" among those waiting to leave.
Speaking from western, government-held Aleppo, she said: "They have been collecting themselves on the points where the buses and the ambulances were waiting for them.
"But now with the operation aborted they had to go back to their houses and this a great concern to us because we know that they are desperate to get out."
Sources on the ground have been offering various explanations for the interruption.
• Government sources said rebels had blocked the evacuation of civilians from two pro-government towns elsewhere in Syria, agreed under the deal.
• World Health Organisation official Elizabeth Hoff said the planned evacuation of the sick and wounded had been halted on Friday on orders from Russian forces, and that no reason had been given.
• Syrian state media said the mission was suspended after rebels tried to smuggle heavy weapons and captives out with them as they left the besieged enclaves.
• Both sides have accused each other of firing on the buses.
Welcome to Friday's coverage on the Aleppo evacuations.
This story has dominated world news coverage this week, as efforts to remove people from the shrinking rebel-held areas in the east of the city have hit repeated obstacles.
A deadlock seemed to have been broken on Thursday, when strings of buses carried thousands of people out.
But now the Syrian government has suspended the evacuation, saying rebels breached the terms of an agreed ceasefire. A condition of the agreement was that civilians were to be moved out of pro-government, rebel-surrounded towns at the same time. But sources in the Syrian government say rebels blocked that evacuation - so the one in Aleppo is off for now.
The UN says there are 50,000 people still in districts of eastern Aleppo that are held by the rebels. Those areas have been under siege for months, and Syrian forces have advanced on them over the past week, bringing most of the city under government control.
A second convoy of evacuees left Aleppo late on Thursday, Syrian state television reported.
The convoy consisted of 15 buses, and would continue in "batches", the report said.
The buses are heading towards rebel territory in western Aleppo province.
Russian news agency Interfax also confirmed the report.
"Just like the previous convoy, it is carrying militants and their family members along a special route ... where they will change onto another form of transport and proceed to Idlib," it said, quoting the Russian Centre for Reconciliation of Opposing Sides in Syria.
The UN Children's Fund (Uncief) is urging all parties to the conflict to allow the immediate evacuation of children from rebel-held Aleppo.
The UK's foreign secretary summoned the Russian and Iranian ambassadors in London over the situation in Syria earlier on Thursday.
Boris Johnson accused both countries of failing in their obligations under international humanitarian law.
"They deserve no credit for the fact that an evacuation appears to be under way," he said in a statement.
"Having inflicted such suffering on the people of eastern Aleppo, Iran and Russia cannot expect praise for allowing some people to escape at the final hour."
Iran and Russia support Syria's government, while the UK backs the opposition.
The pro-opposition Aleppo Media Centre has published some striking video footage of the evacuations, which was shot using a drone.
A senior official from the International Committee of the Red Cross has said it expects to evacuate 2,000 people from rebel-held Aleppo on Thursday - double the number estimated to have left in the first convoy.
The ICRC's Middle East regional director, Robert Mardini, told the Reuters news agency that many more rotations of buses and ambulances would be needed over the next few days.
He said the morning's activity was "the first step - it was a positive one".
UN humanitarian adviser Jan Egeland has expressed concern that the "window" for evacuations may be narrow.
Referencing a video of orphans in Aleppo asking to be rescued, he tweeted: "UN now working with parties on the ground to get these children out of the Aleppo crossfire. The window we have now we may never get again."
In Syrian President Bashar al-Assad's earlier statement, he claimed the "liberation" of Aleppo would be a turning point in world history.
"People do not remember time they remember history ... we say before Christ, and after Christ. We say before revelation on prophet Muhammad, and after the revelation.
"History is not the same before and after," he said.
"I think after liberating Aleppo, we will say not only the Syrian situation, but also the regional and international situation is different - before liberating Aleppo and after it."
Mr Assad paid tribute to the citizens of Aleppo for their resistance and to the Syrian army, the country's new history, he said, started being written by its citizens six years ago.
Aleppo, once Syria’s largest metropolis, will soon join Grozny, Dresden and Guernica by making history for being destroyed a commentary in The Economist says.
Even if many who remain in the last Sunni Arab enclave receive the safe passage they have been promised, "their four-year ordeal has blown apart the principle that innocent people should be spared the worst ravages of war".
"Aleppo’s fall is proof that Mr Assad has prevailed and of Iran’s influence. But the real victory belongs to Russia, which once again counts in the Middle East."
The West "has done no more than rehearse diplomatic phrases" when confronted by Mr Assad’s atrocities, the newspaper says.
"By failing to stand up for what it is supposed to believe in, it has shown that its values are just words - and that they can be ignored with impunity."