The last buses meant to evacuate revels and civilians from Aleppo have been delayed by 24 hours, Syrian activists said.
Some 60 buses to carry the remaining 3,000 evacuees are waiting to leave Aleppo, the British-based Syrian Observatory for Human Rights said.
The Observatory also says 21 buses are waiting to evacuate the sick and wounded from the rebel-besieged Shiite villages of Foua and Kfarya as part of the cease-fire deal reached last week.
Ward Furati, spokesman for Aleppo's Fastaqim rebel faction, says the fighters "won't leave until security of all the civilians has been fully guaranteed."
The evacuations of the remaining civilians in Aleppo will be complete in a maximum of two days, Russian Foreign Minister Sergei Lavrov has claimed.
Speaking at a news conference, the minister said that Russia, Iran and Turkey had used their influence to make the evacuation happen.
It comes as the United Nations increases its presence in the Syrian city to monitor and observe the evacuations.
The evacuation of thousands of people remaining in Aleppo resumed this morning.
All sides of the conflict gave renewed security guarantees to the humanitarian organisation Syrian Arab Red Crescent and the International Committee of the Red Cross as they help with the evacuation.
The evacuation from Eastern Aleppo City will likely take several more days to complete.
Over 15,000 peoplehave so far been able to leave Eastern Aleppo City for rural areas in Aleppo and Idlib.
The UN Security Council has voted unanimously to "carry out adequate, neutral monitoring and direct observation" of the evacuations in eastern Aleppo.
The 15-member council demanded all parties in the conflict to provide UN officials and others with a "safe, immediate and unimpeded access" to those who remain in the Syrian city.
Since midnight, some 4,500 people have left the besieged rebel-held enclave of the city to surrounding villages.
The mother of a seven-year-old girl who tweeted about living conditions under the Syrian regime has spoken of her relief to finally reach safety.
Bana al-Abed attracted over 300,000 Twitter followers by providing harrowing updates on her living conditions and near-death experiences when she was growing up in besieged eastern Aleppo.
On Sunday, Bana and her mother Fatemah were some of 12,000 people to be evacuated as part of a deal to return the city to government control.
Holding her arm around her daughter, Fatemah told the activist-run Qasioun News at her relief at leaving, but also the regret of being forced out of her home city and living as a refugee.
We created our Twitter [account] to tell all the world what is happening there [in eastern Aleppo].
We are happy because our voice reached all the world. We are free.
We are feeling - I am sad because I leave my country, I left my soul there. I want to take our freedom there, not to be like a refugee in other countries. I want for my kids a good future. But this is the matter here.
They make us leave our country. We can't stay there because there is a lot of bombs and no clean water, no medicine.
They even targeted hospitals and schools. When we get out, we had a lot of suffering, because we stayed almost 24 hours in a bus without water and food and anything.
We stayed like prisoners, a hostage.
Finally, we arrived here and we thank God and we thank all our friends who have supported us.
Dozens of children who were trapped in an orphanage in the rebel-held enclave of east Aleppo have been evacuated, UNICEF said.
Geert Cappelaere, regional director for the United Nation's Children's Fund, said: "This morning, all 47 children trapped in an orphanage in east Aleppo were evacuated to safety, with some in critical condition from injuries and dehydration."
He said UNICEF and other agencies were assisting in reuniting other evacuated children with their families, and giving them winter clothes and medical care.
Some 12,000 people have been evacuated from east Aleppo in the past few days, according to Turkey's foreign ministry.
The figure includes 4,500 civilians who have managed to leave the city since midnight.
Mevlut Cavusoglu said: "Including 4,500 people in east Aleppo since midnight, 12,000 civilians in total were evacuated so far to the area under control of opposition."
The evacuations are the result of intense negotiations between Turkey - which backs some large rebel groups - and Russia, who support President Bashar al-Assad's regime in Syria.
A seven-year-old girl who gained more than 300,000 followers after tweeting about her ordeal in eastern Aleppo has managed to leave the besieged city, according to an aid organisation.
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Bana al-Abed was included in a convoy of busses that left the city over the past week.
Her departure was confirmed by the head of the Syrian-American Medical Society aid group.
In a tweet on Monday, Ahmad Tarakji said Bana was among "many children" who have arrived in the Aleppo countryside.
A convoy of busses carrying evacuees from eastern Aleppo has arrived at the town of al-Rashideen.
The Syrian Observatory for Human Rights said the new convoy of 21 busses had arrived at the insurgent-held district early on Monday.