"The teams of civil defense are working in besieged cities in most areas, like Aleppo city, besieged for more than two months and we are having difficulties securing fuel and the equipment needed for work", he told The Associated Press in a Skype interview.
Germany's Foreign Ministry says it is increasing financial support for the Syria Civil Defense group, also known as the White Helmets.
An image taken from video posted online by Syrian activists shows members of the "White Helmets" volunteer rescue service and others removing an injured person from the rubble of the al-Quds hospital in southern Aleppo, which was destroyed by an airstrike, April 28, 2016. Many people were reportedly killed or wounded in strike.
The Syria Civil Defense group, also known as the White Helmets, was cited "for their outstanding bravery, compassion and humanitarian engagement in rescuing civilians from the destruction of the Syrian civil war". He said the attack on civil defense centers had hindered their work because some of their vehicles had been destroyed.
A Syria Civil Defense member carries a child to safety in this undated photo.
An unnamed Syrian military official was quoted by state media on Friday as saying that airstrikes and shelling in Aleppo would continue for an extended period and "include a ground offensive" into rebel-held areas. "Surrender now or you will meet your inevitable destiny", read one leaflet, which had a photo of the body of a bearded militant with a rocket-propelled grenade next to him.
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"We have four centers in eastern Aleppo". The Local Coordination Committees, another monitoring group, said 49 were killed on Saturday alone.
"We are deeply anxious by the high numbers of wounded reported by the hospitals we support, and also know that in many areas the wounded and sick have nowhere to go at all - they are simply left to die". The pro-government Addounia TV blamed the rebels for targeting the station in Bab al-Nairab, which feeds both sides of the contested city. The station said pumping from the station has ceased, but said work had began to fix it. It was not immediately possible to verify or assess the extent of the damage or independently confirm who hit it.
The air campaign late Thursday night and Friday morning comes as Syria's military command announced it is launching operations in Aleppo's rebel-held eastern quarters, raising concerns of imminent ground operations.
Aleppo, the country's second biggest city, has been divided among government troops, rebel militias, Islamic extremists and Kurdish fighters since 2012.
Syrian troops captured a rebel-held area on the edge of Aleppo on Saturday, tightening their siege on opposition-held neighborhoods in the northern city after what residents described as the heaviest air bombardment of the 5 ½-year civil war.
"What did they achieve in Syria?" he said. After a week of diplomatic talks and attempts to seek consensus, developments on the ground in Syria seem to have overshadowed prospects for bringing about calm.