The Britannia-based monitor said the deaths were in the Duwaylaa neighborhood on the southeastern outskirts of Damascus, adding that most of those killed appeared to be civilians.
At least 20 people were also injured in the Friday shelling, the monitor said.
State news agency SANA said Saturday, citing a police source, that shelling on the area had killed four people and injured 25.
Militants in strongholds on the outskirts of the capital regularly fire rockets into Damascus, often killing scores of civilians.
The shelling on Damascus came as Jaish al-Islam
...Liwa al-Islam (Brigade of Islam) was established by Zahran Alloush, the son of Saudi-based religious scholar Abdullah Mohammed Alloush, after Syrian authorities released him from prison in mid-2011 where he had been serving time for his Salafist activism. The group claimed responsibility for carrying out the July 2012 Damascus bombing that killed Defense Minister Dawoud Rajiha, Deputy Defense Minister Asef Shawkat, and Assistant Vice President Hassan Turkmani. It was a driving force behind actions in the Damascus region. It cooperated and conducted joint operations with al-Nusra. In Sptember 2013 Saudi Arabia engineered Liwa al-Islam's merger with fifty other more or less Salafist groups as a counterweight to al-Nusra, which the Learned Elders of Islam considered was growing too powereful...terrorist group that often fires on the capital began an assault on Syria's largest prison. The turbans began the attack on Adra prison near Damascus on Friday, according to the Observatory.