It comes as the United Nations General Assembly has voted to establish a special team to investigate, and prepare cases on, war crimes and human-rights abuses committed in the war.
In the northern Syrian city of Al-Bab, a video published by the self-proclaimed Islamic State purports to show heavy shelling by Turkish forces.
The Syrian war is still raging after nearly six years and more than 400,000 deaths.
For the past week, a perilous evacuation process has been taking place to remove citizens and rebel fighters from the besieged city of Aleppo.
Now, President Bashar al-Assad has been handed his biggest victory as he claims his forces have seized total control of what was the country's largest city.
In a statement broadcast on Syrian television, the army said it has re-established what it calls "security" in Aleppo.
Syria's General Command of the Military and Armed Forces says the victory is a turning point in what it calls "the war against terror."
"By virtue of the pious blood of our martyrs and the heroism and sacrifice of our fearless armed forces and its reserves and allies, and the determination of our people, the General Command of the Military and Armed Forces declares the return of security and safety to the city of Aleppo following its liberation from terror and the departure of the terrorists who remained from the city."
The United Nations special envoy for Syria, Staffan de Mistyra, says renewed political negotiations on the war will take place in Geneva in February.
Mr de Mistyra says a high priority is the immediate safety and welfare of those evacuated from Aleppo.
"Now the next steps, of course, are to look at where do the people who are being evacuated go and whether they, in the winter, will be actually not suffering further. Because, some of them are going to west Aleppo, a few. Many, many have gone to the rural part of Aleppo, which is in the armed-controlled areas of the armed opposition and, therefore, again a question about how to make sure that the humanitarian aid from the UN can reach them. And many have gone to Idlib, which could be, in theory, the next Aleppo. So we have to look forward."
Meanwhile, Syria's principal allies, Russia and Iran, began consultations with Turkey this week on a political settlement -- without even consulting the United Nations.
The United Nations has been criticised for its inability to act and intervene throughout the crisis but has now passed a raft of new resolutions.
They call for an international, impartial and independent mechanism to be formed to prepare war-crimes cases in Syria for prosecution in a future court.
The General Assembly adopted a Liechtenstein-drafted resolution to establish the independent team, with 105 in favour, 15 against and 52 abstentions.
Syria's ambassador to the United Nations, Bashar Ja'afari told the General Assembly the war-crimes resolution violates the UN charter.
Mr Ja'afari says any investigation would be biased, and he has accused other countries of supplying weapons in the war.
"The contents of the draft resolution presented to you today proves considerable hypocrisy and the enormous gap between the theory and the practice of the sovereignty of member states."
The adoption of the resolution comes after a UN panel concluded warplanes had bombed a humanitarian-aid convoy in Syria three months ago.
Dr Simon Adams is a war-crimes expert at the New York-based Global Centre for the Responsibility to Protect.
He has told Al Jazeera television, while it is welcome news that the United Nations will investigate war crimes, it is too little and too late for many.
"I think it's a signal of how completely despondent the international community is about the way that the UN Security Council has behaved. The UN Security Council has absolutely failed in its mandated responsibilities to uphold international peace and security, with regard to Syria, and its responsibility to protect the people of Syria themselves and to hold perpetrators accountable."
British-based international-law specialist Rodney Dixon says the UN resolution is a historic decision.
But he has told Al Jazeera, while it is a very important step in taking investigations forward, there are still questions to be answered.
"Of course, the big question is what happens the day after. Will a court be established, and how will that be done? But the critical first step has been taken."
