The Russian Foreign Minister Sergei Lavrov has said the Syrian army has suspended active military operations in eastern Aleppo because a large civilian evacuation effort was underway, according to reports.

I think what is happening now is shameful for the whole of humanity Tawfik Chamaa Union of Syrian Medical Relief Organisations

He described it as the largest operation yet to remove civilians from eastern districts.

The Syrian army’s advance in Aleppo reportedly slowed on Thursday as allied forces attacked the last rebel-held areas. Army gains have lost momentum after the advance of recent days in which the historic Old City was recaptured.

However victory was still in sight after President Assad said that re-taking the nation’s second city would change the course of the war.

His forces have captured most of Aleppo’s eastern territory, but an estimated 200,000 civilians and some 8,000 rebels are still thought to be trapped in the siege.

Earlier on Thursday, the United Nations’ humanitarian adviser for Syria had some harsh words about international efforts to evacuate civilians.

Warning that 150,000 people faced “extermination”, Jan Egeland said five months of negotiations over aid plans had produced “nothing” – adding that it was up to the United States and Russia to try to coordinate a deal.

The two countries were still “poles apart” in how they viewed events in Syria, he said after a meeting in Geneva. Lavrov said later it had been agreed that Russian and US military experts would meet in Geneva on Saturday to discuss Aleppo.

According to the Union of Syrian Medical Relief Organisations, some 1,500 people needed medical evacuation from Aleppo, including 500 “seriously wounded”.

“All the achievements of humanity to uphold these conventions and other principles to protect civilians, hospitals and medical staff have been violated every day in Syria for five years. I think what is happening now is shameful for the whole of humanity,” said the organisation’s coordinator, Tawfik Chamaa.

The International Committee for the Red Cross says it has evacuated nearly 150 disabled civilians and others from Aleppo’s Old City – an operation made possible since fighting calmed down.

Earlier, the Syrian government ignored a rebel ceasefire proposal as the army moved frightened civilians out of a southeastern district of Aleppo, Sheikh Lutfi, one of several neighbourhoods recaptured from rebels.

There have been disagreements over where civilians should go. The UN’s humanitarian adviser Jan Egeland said opposition groups simply wanted people to be allowed to leave eastern Aleppo, with no strings attached.

Russia has wanted the area’s citizens to leave via four humanitarian corridors.

The head of Britain’s intelligence agency MI6 has strongly criticised Russia over its role in Syria. Speaking in London on Thursday, Alex Younger cast President Putin’s intervention on the side of President Assad as a crude tactical ploy.

“In defining as a terrorist anyone who opposes a brutal government, they alienate precisely the group that has to be onside if the extremists are to be defeated,” he said. “Russia and the Syrian regime seek to make a desert and call it peace.”