Zahroun Alloush founded Jaysh al-Islam
Founder Zahroun Alloush, 44, was among those killed when rockets hit a meeting place, rebels and the Syrian army said.
The Saudi-backed Islamist group is one of the biggest factions and is dominant in the Eastern Ghouta countryside.
It recently joined an opposition summit in Riyadh which produced a framework for peace talks with the government.
Ten rockets struck as Jaysh al-Islam commanders met, Saudi-funded al-Arabiya TV reported. The group’s deputy leader was also killed, al-Arabiya said.
Russia, a key ally of Syrian President Bashar al-Assad, has been waging an air campaign in Syria since the end of September.
Moscow insists it has been targeting so-called Islamic State, but rebels and Western officials say the Russian strikes have mainly been hitting other groups.
Jaysh al-Islam, whose fighters number tens of thousands, took part in the conference in the Saudi capital which agreed a common approach among disparate rebel groups for UN-backed peace talks planned for January.
Syria and Russia dismissed the meeting, saying the groups did not properly represent the opposition and that those that did attend were unacceptable.
BBC
