United Nations' Syria envoy Staffan de Mistura on Thursday called on Syria and Russia to halt brutal strikes on eastern Aleppo if fighters from the former Al-Nusra Front, now known as Fateh al-Sham Front, left the city, even offering to escort them out himself.

"If Nusra leaves with its arms in the direction of Idlib, where its main forces are based, then for the sake of saving Aleppo we are ready to support such an approach and would be ready to call on the Syrian government to agree to this," Lavrov said in an interview with Russia's Channel One television.

The presence of former Al-Qaeda affiliate Nusra in rebel-held eastern Aleppo is used by Russia as the main justification for its air strikes on the besieged city in support of the Syrian ground offensive.

Despite opening up the possibility of Moscow halting its attacks, Lavrov set strict conditions for any Nusra fighters who remain behind in Aleppo -- insisting they would have to sign official documents renouncing any ties with the group.

"Then the government law enforcement structures from the police and the armed opposition could form some sort of joint law enforcement bodies," he said.

Syria government forces have made their first real gains in years into rebel-held Aleppo in the latest offensive after the collapse of a truce hammered out by the United States and Russia.

The assault on the strategically vital divided city has sparked Western accusations of possible war crimes, with de Mistura warning that east Aleppo could be "totally destroyed" by the year's end.

The UN Security Council is to hold an emergency meeting later Friday at the request of Russia to receive a briefing from de Mistura.

Council members are also discussing a French-drafted resolution calling for a ceasefire in Aleppo; AFP reported.

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