Civilians living in besieged areas of Aleppo consider the situation to be a “living hell” as they are enduring lack of food and water.
Humanitarian missions found it difficult to find their way inside to provide aid to survivors of devastating air strikes from the Syrian regime. Meanwhile, rebel-held frontlines remained vulenrable to Russian air strikes overnight.
The attacks had allowed Syrian regime forces to occupy the north of the city.
“The army high command calls all armed fighters in the eastern neighbourhood of Aleppo to leave these neighbourhoods and let civilian residents live their normal lives,” said a statement, carried by state news agency Sana on Sunday.
Syrian government forces have been trying for months to recapture the city’s eastern half, which has long been a major opposition stronghold.
“I am deeply alarmed by the ferocious pummelling of eastern Aleppo city,” Mr O’Brien, UN under-secretary for humanitarian affairs, said in a statement.
“Indiscriminate bombing and shelling continues in a shocking and unrelenting manner, killing and maiming civilians, subjecting them to a level of savagery that no human should have to endure.”
The healthcare system in eastern Aleppo had been “all but obliterated”, he added.
On Saturday, air strikes hit Aleppo’s main trauma M10 hospital for the third time in a matter of days, medical workers say.
“The hospital is now out of service completely,” radiologist Mohammad Abu Rajab was quoted by Reuters as saying.