Russia has said it is “ready” for talks with the US to allow for the withdrawal of rebels from eastern Aleppo as the Syrian government’s advance continues.

President Bashar al-Assad’s forces and allies from Russia, Iran and Hezbollah are estimated to have seized 60 per cent of territory formerly controlled by the opposition in a bloody campaign marred by allegations of war crimes on both sides.

“We are immediately ready to send out military experts, and diplomats to Geneva in order to agree mutual actions with our American colleagues to ensure the pullout of all the rebels without exclusion from eastern Aleppo,” said Sergei Lavrov, the Russian foreign minister.

The United Nations and humanitarian groups have demanded safe passage for civilians to leave opposition areas amid fierce fighting and bombardment, with hundreds reportedly killed since the regime’s offensive started last month.

At least 45 Syrian refugees killed by regime missile while trying to flee Aleppo

Russia has demanded all “terrorists” – a term used by Syria to refer to all rebels – withdraw and calls by the UN for jihadi groups to separate themselves from more moderate elements have failed.

A statement published by an alliance calling itself the Opposition Council for Aleppo on Saturday denied making any agreement with the Syrian government or “other parties” and vowed to fight on.

Zakaria Malahifji, from the Fastaqim rebel group, told Reuters: “I asked the factions, they said 'we will not surrender'.

“The military commanders in Aleppo said ‘we will not leave the city. There is no problem with corridors for civilians to leave, but we will not leave the city’.”

Staffan de Mistura, the UN special envoy for Syria, said some rebel groups had been preventing civilians leaving their territory and told the Security Council he hoped a “formula for stability” could be found to end the violence.

In pictures: Aleppo bombing Show all 14 1 /14 In pictures: Aleppo bombing In pictures: Aleppo bombing Bombing in Aleppo Smoke rises after airstrikes on the rebel-held al-Sakhour neighborhood of Aleppo, Syria April 29, 2016. Reuters In pictures: Aleppo bombing Bombing in Aleppo A Syrian family runs for cover amid the rubble of destroyed buildings following a reported air strike on the rebel-held neighbourhood of Al-Qatarji in the northern Syrian city of Aleppo, on April 29, 2016. AFP/Getty Images In pictures: Aleppo bombing Bombing in Aleppo A man reacts as he stands on blood stains at a site hit by airstrikes in the rebel held area of Aleppo's al-Fardous district, Syria, April 29, 2016. Reuters In pictures: Aleppo bombing Bombing in Aleppo The damage of the airstrikes in the rebel-held area of Aleppo on April 28 Reuters In pictures: Aleppo bombing Bombing in Aleppo The damaged the Medecins Sans Frontieres (MSF)-backed al-Quds hospital after it was hit by airstrikes, in a rebel-held area of Syria's Aleppo Reuters In pictures: Aleppo bombing Bombing in Aleppo Syrians evacuate an injured man amid the rubble of destroyed buildings following an air strike on a rebel-held of Aleppo on April 29, 2016. AFP/Getty Images In pictures: Aleppo bombing Bombing in Aleppo People inspect the damage at a site hit by airstrikes, in the rebel-held area of Aleppo's Bustan al-Qasr AP In pictures: Aleppo bombing Bombing in Aleppo A man leads a woman in tears and child out of the scene after airstrikes hit Aleppo AP In pictures: Aleppo bombing Bombing in Aleppo Civil defence members search for survivors after an airstrike at a field hospital in the rebel held area of al-Sukari district of Aleppo Reuters In pictures: Aleppo bombing Bombing in Aleppo A Syrian boy is comforted as he cries next to the body of a relative who died in a reported air strike in the rebel-held neighbourhood of al-Soukour in the northern city of Aleppo Getty Images In pictures: Aleppo bombing Bombing in Aleppo A Syrian family walks amid the rubble of destroyed buildings following a reported air strike in the Bustan al-Qasr rebel-held district of the northern Syrian city of Aleppo Getty Images In pictures: Aleppo bombing Bombing in Aleppo Syrian civil defence volunteers and rescuers remove a baby from under the rubble of a destroyed building following a reported air strike on the rebel-held neighbourhood of al-Kalasa in the northern Syrian city of Aleppo Getty Images In pictures: Aleppo bombing Bombing in Aleppo Syrians help a wounded youth following an air strike on the Fardous rebel held neighbourhood of the northern Syrian city of Aleppo Getty Images In pictures: Aleppo bombing Bombing in Aleppo Syrian civil defence volunteers evacuate people from a damaged building following a reported airstrike in the rebel-held neighbourhood of Tareeq al-Bab in the northern city of Aleppo

He has called for the departure of any groups falling until the UN’s definition of terrorists but days after a range of moderate, Turkmen, Islamist and jihadi groups pledged to unite against Assad’s forces, that prospect looked less likely than ever.

Speaking at a conference in Rome, Mr de Mistura predicted eastern Aleppo could fall by the end of the year, saying: “Aleppo is not going to stay that long.”

“I was feeling it would be a terrible battle ending up by Christmas/New Year. I hope the battle will not take place, that there will be some type of formula,” he said, alluding to “informal negotiations”.

Almost 30,000 people have been displaced by the fighting, 18,000 of them moving to government-held areas and a further 8,500 going to the Kurdish-controlled neighbourhood of Sheikh Maqsoud.

Tens of thousands are believed to remain in rebel-held eastern Aleppo, under heavy bombardment and with supplies of food, fuel and healthcare critically low after several hospitals were destroyed.

The UK-based Syrian Observatory for Human Rights said at least three people were killed and 10 injured by air strikes in the al-Shaar neighbourhood on Saturday, leaving several people in a critical condition.

A general view taken from the government-held side of Aleppo shows smoke billowing during fighting between Syrian regime forces and rebel fighters in east Aleppo, on December 3, 2016. (AFP/Getty) (AFP/Getty Images)

The White Helmets volunteer group said a gathering of displaced people had been struck and put the death toll at more than six, while Syrian state media said four civilians were killed in regime-held areas by rebel rocket attacks and shelling.

Around 310 civilians have been killed in the government’s assault since 15 November, the Observatory said, with at least 69 civilians killed in the same period by rebel fire on regime-held west Aleppo.

The Tariq al-Bab district was the main focus of fighting overnight, with rebels claiming they had repelled a government assault but photos showing soldiers flashing victory signs in its rubble-strewn streets.

Regaining control of Aleppo, formerly Syria’s most populous city, would be a symbolic victory for President Assad’s government in the fifth year of the civil war.

The government has gained ground elsewhere by reaching numerous local agreements with rebels in besieged areas, giving them safe passage to the insurgent-held province of Idlib in exchange for their surrender.

Federica Mogherini, the EU foreign policy chief, warned that Aleppo’s fall would not end the war in Syria, where Isis, the former al-Qaeda affiliate Jabhat al-Nusra, Kurdish groups and numerous rebel factions are competing for territory.

“This will only make things worse and, by the way, I am convinced the fall of Aleppo will not end the war,” she said.