At least 82 civilians have been shot and killed "on the spot" in rebel held Aleppo, the UN has said, as pro-regime forces entered the eastern enclave of the Syrian city.

The UN's human rights agency said it has received credible reports outlining that 11 women and 13 children were among those killed in the four Aleppo districts still held by the rebels.

UN spokesperson Rupert Colville said reports recount pro-government forces entering homes where they carried out the shootings. They apparently occurred on the evening of 12 December although the exact whereabouts is unknown, the Associated Press reported.

As the crisis worsens, UK ministers will be urged to act on the dire humanitarian situation in Aleppo in an emergency debate in the commons today as MPs warned those civilians still in the devastated city have nowhere to hide.

The debate, called for by Former Cabinet minister Andrew Mitchell, comes as Syrian government forces – backed by Russia – claimed to have retaken 99% of Aleppo from rebel forces.

Mitchell is to call on the UK to use its diplomatic muscle to broker a ceasefire in Aleppo. He will ask the government to secure a 24-hour suspension of the fighting to enable civilians to be rescued from, what he has described as, a "hell" inside the city.

"The debate would enable us to explore with the Government how Britain's immense diplomatic muscle, the finest foreign service in the world, can do more to secure a deal that will ensure a ceasefire for at least 24 hours to enable innocent civilians to be rescued from the hideous circumstances which now prevail in east Aleppo," The Press Association quoted Mitchell as saying.

"Many of these terrified civilians trapped in this hell hole, which now resembles Stalingrad at the end of its destruction, are children. They have few places to hide," he said.

Syrians celebrate with national flags in an Aleppo's regime-held district near the al-Shuhaba roundabout, after rebel fighters retreated into a small pocket of their former bastion in the face of new army advances AFP/ Getty Images

On 12 December, Bashar al-Assad's forces on 12 December confirmed that at least 99% of the city was recaptured as insurgents from groups such as Fatah Halab (Aleppo Conquest), the Free Syrian Army and the al-Qaeda-linked Jabhat Fateh al-Sham (formerly known as the Al-Nusra Front) all retreated.

Rami Abdulrahman, head of the UK-based monitor the Syrian Observatory for Human Rights, said: "It is just a matter of a small period of time until it's a total collapse."

Already the massive gains made by pro-Assad forces have marked a pivotal shift in the Syrian Civil War in 2011. Securing Aleppo – the country's most populous city before the beginning of the war – will be the government's most decisive victory.

As some 150,000 civilians are said to remain in the last areas held by the rebels, the International Committee of the Red Cross (ICRC) has warned against a deepening humanitarian catastrophe in Aleppo.

"A deepening humanitarian catastrophe and further loss of life can be averted only if the basic rules of warfare – and of humanity – are applied.

George Ourfalian
A general view taken from Aleppo's citadel show fumes rising following shelling on neighbourhoods in the old city on 7 December George Ourfalian/ AFP

"We urge the parties to consider the fate of civilians trapped by the ongoing fighting and do their utmost to spare and protect them. This may be the last chance to save lives.

"For more than a week, the International Committee of the Red Cross (ICRC) has been in touch with all sides to find a humanitarian solution that could prevent further human suffering.

"These efforts have so far failed to yield results, and time is running out," the medical NGO said in a statement.

The fall of Aleppo timeline: How Assad captured Syria's biggest city