Russia's ambassador to the United Nations has said military action has ceased in eastern Aleppo which if confirmed, would bring to an end four years of fighting.

Vitaly Churkin said the Syrian government was now in control of the areas of the city that had been held by rebels.

"According to the latest information that we received in the last hour, military actions in eastern Aleppo are over," Churkin told an emergency session of the UN Security Council.

Earlier, he said that a deal has been agreed for rebel groups to evacuate the areas of east Aleppo they still occupy.

"My latest information is that they indeed have an arrangement achieved on the ground that the fighters are going to leave the city," Churkin said, adding that rebel groups are scheduled to start leaving the city "within hours".

Tens of thousands of civilians remain trapped in rebel-held areas of the city besieged by Syrian government forces backed by Russian air strikes.

A rebel official from the political office of the Nurredin al-Zinki group said the deal included allowing civilians to leave.

"An agreement has been reached," Yasser al-Youssef told AFP. "The first stage will be the evacuation of civilians and wounded, within hours, and afterwards fighters will leave with their light weapons."

Those leaving will be allowed to travel to other rebel-held territory in the west of Aleppo province or neighbouring Idlib province, he said.

Churkin said the deal, agreed between the Russian military and Turkish intelligence, meant the Syrian government would be regaining control of the city, so there was no need to for residents to leave their homes.

It comes hours after UN agencies reported that pro-government forces had been summarily killing civilians in Aleppo, including women and children.

Unicef added that as many as 100 children may be trapped inside a building under heavy attack in the city.

Parts of Aleppo were seized by rebel groups after the 2011 uprising against the regime of President Bashar al-Assad.

In recent months, pro-government forces launched a major offensive to regain control of the city, with Russia's military saying 98% of territory was back in government hands.