At the start of the week, a coalition of rebels and militants including a former al-Qaeda affiliate surrounded the only regime base in Eastern Ghouta, which lies east of Damascus and has been under a crippling regime siege since 2013.
Hundreds more patients are in urgent need of evacuation from the enclave, where there are only 107 doctors and severe shortages of medical supplies.
Eight people died in the village of Hammuriye, while two others were killed in Medyere, and three civilians were also killed in Arbin.
Nine women and two children were among the 18 people killed, it said, adding that the number might rise because some of the injured were in a critical condition.
Residents including members of the White Helmets rescue group rushed to rescue the wounded. Since then, hundreds of thousands of people have been killed and more than 10 million others displaced, according to United Nations officials.
The Britain-based Syrian Observatory for Human Rights said 17 people were killed Saturday, 12 of them in the suburb of Hamouriyeh.
That bloodshed came after Abdel Rahman said Russian and regime strikes on Wednesday claimed the lives of 29 civilians in eastern Ghouta.
There was no immediate confirmation by the Russian military, which is providing air support to government forces fighting rebels.
Earlier this week, rebels overran a major military base in the heart of the Harasta district, triggering heavy air strikes on surrounding rebel-held territory.
Four bombs hit two buildings in a residential area, and the civilians were within.
"The Kommersant report on alleged "actual destruction" of seven Russian war planes at Hmeymim air base is fake", TASS said, citing the ministry.