Updated on October 6 at 2:37 p.m. EST

NEWS BRIEF If the intensified bombing campaign by Russian and Syrian forces in Aleppo doesn’t cease, the once vibrant eastern part of the Syrian city may face total destruction by the end of the year, the United Nations warned Thursday.

“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,” Staffan de Mistura, the UN envoy to Syria, said Thursday in Geneva. “We are talking about the old city in particular.”

De Mistura’s appeal to Moscow and Damascus follows the latest offensive by both countries to reclaim the eastern part of the divided city, considered the last major rebel stronghold whose takeover could mark a key turning point in the country’s five-year civil war. The intensified airstrikes on the eastern half of the city, where 250,000 civilians remain, has resulted in unprecedented destruction—the kind de Mistura said the UN would not ignore.

“There is only one thing we are not ready to do: be passive, resign ourselves to another Srebrenica, another Rwanda, which we are sadly ready to recognize written on that wall in front of us, unless something takes place,” the UN envoy said.