The UN's Syria envoy on Thursday made an impassioned appeal to save eastern Aleppo, warning the city faced total destruction and urging Islamist fighters to leave so civilians can get aid.
"In maximum two months, two and a half months, the city of eastern Aleppo at this rate may be totally destroyed", Staffan de Mistura told reporters in Geneva.
The rebel-held eastern part of Aleppo has been hammered by a Russian-backed government offensive, including multiple attacks on hospitals.
De Mistura noted that the presence of Al-Nusra fighters in the city has been used as a justification by Moscow and Damascus for the continued assault.
The former Al-Nusra Front has recently changed its name to Fateh al-Sham Front following a break with Al-Qaeda, but many still see the two groups as tied.
"Can you please look at my eyes", de Mistura said in a direct appeal to Nusra leaders, before pleading with them to quit Aleppo.
"If you decide to leave in dignity and with your weapons... I personally am ready physically to accompany you," the UN envoy said.
The UN estimates that 275,000 civilians are under siege in east Aleppo, with aid deliveries all but impossible since government forces seized the last supply route in July.
De Mistura accused Nusra fighters of holding "hostage" desperate civilians in need of life-saving relief by refusing to withdraw from the city.
He said a UN analysis estimated there were 900 Nusra fighters in east Aleppo, out of a total of some 8,000 rebels.
The Syrian Observatory for Human Rights, a monitoring group, has however said that anti-government fighters in east Aleppo number 15,000 -- only 400 of whom belong to Fateh al-Sham Front.
- Appeal to Russia, Assad -
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In a second appeal to Russia and Syrian President Bashar al-Assad's government, the UN envoy asked if they were truly prepared to bring about the ruin of Aleppo, once Syria's economic powerhouse.
"Or, are you rather ready to announce an immediate and total aerial bombing halt if Nusra leaves?" de Mistura asked.
He warned that eastern Aleppo risked joining the ranks of the 20th century's worst tragedies, making comparisons to the massacre at Srebrenica and the Rwandan genocide.
Aleppo has been split between a government-controlled west and rebel-held east since 2012.
Following the collapse of the latest ceasefire negotiated by Washington and Moscow, Assad's forces on September 22 renewed their assault on eastern Aleppo.
De Mistura said 376 people had been killed and more than 1,200 injured since the bombardments restarted.
The surge in fighting, including an attack on the area's biggest hospital, spurred the United States to suspend its cooperation with Russia on the Syrian peace effort.
Russia has denied all responsibility for hospital attacks in the city.
Russia and the US have also co-chaired the 20-member International Syria Support Group (ISSG), which includes a humanitarian taskforce and a body that monitors ceasefire violations.
De Mistura conceded that widening cracks in US-Russia relations had been "a serious setback" for the ISSG's work, but said humanitarian taskforce members voted on Thursday to press on.
On the ceasefire body, de Mistura said the question of its future was less pressing given the raging violence.
"We don't have anymore a cessation of hostilities."