Story highlights Russia urged civilians to evacuate during the ceasefire

The UN said it was unable to carry out medical evacuations due to security risks

(CNN) A brief, unilateral ceasefire effectively ended on Sunday with the resumption of airstrikes against the besieged, rebel-held portion of eastern Aleppo.

Residents said warplanes began bombing the city in the latter half of Sunday.

"The bombing started again," a Syrian White Helmet rescue worker named Ismail Abdullah told CNN by phone from eastern Aleppo.

"I heard a lot of bombing in the night. They were airstrikes."

Civilians urged to evacuate

Read More