Staffan de Mistura said military activity in the city meant thousands of citizens were likely to be killed
The United Nations' Special Envoy to Syria has warned that part of Aleppo could be totally destroyed in just ten weeks.
Staffan de Mistura said that "cruel, constant" military activity in the east of the city meant that thousands of citizens - not terrorists - were likely to be killed.
The besieged population of 275,000 - including 100,000 children - is in desperate need of aid supplies.
Speaking at a news conference in Geneva, he said: "The bottom line is in a maximum of two months, two and a half months, the city of eastern Aleppo at this rate may be totally destroyed.
"We are talking about the old city in particular."
He said no-one could deny that the situation in Syria and Aleppo was an "emergency".
He said he was willing to go to the city and escort around 900 Islamist fighters away from the area, if it meant an end to the bombardment by Syrian and Russian forces.
The Russian news agency Tass said the country's Deputy Foreign Minister, Mikhail Bogdanov, supported the idea.
The militants are from the Fatah al-Sham Front - formerly known as the Nusra Front - which has been linked to al-Qaeda.
The United Nations considers the Nusra Front to be a terrorist group.
Mr De Mistura said the Islamists would "need some guarantees" that safe passage to Idlib province was a possibility.
Addressing them directly, he said: "Can you please look at my eyes.
"If you decide to leave with dignity... I am personally ready to physically accompany you."
Referring to Syria and Russia's "aerial bombing", he warned both countries not to use the Islamists' presence as an "easy alibi" to destroy the area.
He said that history would judge such action harshly.