Story highlights "Hundreds of critical medical evacuations are urgently required," a U.N. official says

The regime says it will guarantee the safe departure of rebels who leave Aleppo

(CNN) The fierce battle for Syria's largest city intensified Sunday, with a civilian hospital attacked and pro-regime forces gaining ground in Aleppo.

Government forces now control the strategic area around al-Kindi Hospital in northern Aleppo, pro-regime media and activists said, strengthening their push toward the rebel-held eastern part of the city.

While the regime gained power on the ground, more airstrikes fell on rebel-held eastern Aleppo Sunday, several residents told CNN.

"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," United Nations aid chief Stephen O'Brien said Sunday.

Photos: Heartbreaking images following Aleppo airstrike Photos: Heartbreaking images following Aleppo airstrike A Syrian family leaves the area following a reported airstrike on Friday, September 23, in rebel-held east Aleppo. Following the airstrike, recovery teams from Syria Civil Defense, known as the White Helmets, began working to free the trapped and recover the dead, including small children. Hide Caption 1 of 7 Photos: Heartbreaking images following Aleppo airstrike Hide Caption 2 of 7 Photos: Heartbreaking images following Aleppo airstrike This photo was released by the volunteer group Syria Civil Defense of the bodies of a man, with his knee pulled up near his face, and a child covered in dust after they were killed in the airstrike. Hide Caption 3 of 7 Photos: Heartbreaking images following Aleppo airstrike The volunteers work to recover the bodies the man and child. Hide Caption 4 of 7 Photos: Heartbreaking images following Aleppo airstrike A Syrian man carries the body of his nephew, recovered from the rubble. Hide Caption 5 of 7 Photos: Heartbreaking images following Aleppo airstrike The volunteers remove an infant's body from the destroyed building. Hide Caption 6 of 7 Photos: Heartbreaking images following Aleppo airstrike A Syrian woman carries the body of her infant after he was recovered. Hide Caption 7 of 7

The M3 hospital was hit Sunday, a day after the city's M10 hospital was bombed for the second time in a week.

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