Lieutenant General Hussein Ishaq succumbed to the injuries he suffered in the military assault on an airbase near the town of Mleiha in the outskirts of capital Damascus, according to press reports on Sunday.
The Syrian government has not yet reacted to the news.
Meanwhile, Syrian government forces maintain full control of Damascus, but the armed insurgents still hold a few towns and villages on the outskirts of the city.
Syrian troops have in recent months gained the upper hand in battles against the foreign-sponsored armed groups.
On May 12, a final group of foreign-backed Takfiris left the western city of Homs as part of a deal reached between Damascus and the militants on May 4.
The safe exit of militants from Homs was part of the agreement which was brokered by Iran, Russia and the United Nations.
The deal also brought almost all major districts of the city under the control of government forces. The Syrian government’s talks with the militants came as part of efforts to facilitate access to the people trapped in conflict zones.
The agreement required the militants to allow aid into two northwestern towns of Kafr Nabl and al-Zahraa. The militants also agreed to release dozens of soldiers and civilians held hostage.
Syria has been gripped by deadly violence since March 2011. Over 150,000 people have reportedly been killed and millions displaced due to the violence fueled by the foreign-backed militants.
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