Omar Farouq al-Turki was killed in clashes that erupted between ISIL members and rival militants from the al-Nusra Front in the region, reports said on Saturday.
Earlier in the day, heavy clashes were reported between the two foreign-backed Takfiri groups in the oil-rich province of Deir al-Zour in eastern Syria.
The al-Qaeda-linked al-Nusra Front has accused the ISIL of attacking its bases in Deir al-Zour, occupying several towns and villages.
The ISIL has besieged Deir al-Zour to kill al-Nusra leader Abu Mohammad al-Julani, who has reportedly taken refuge in the area.
Infighting among militant groups in northern Syria has escalated in recent months.
Last February, the so-called Syrian Observatory for Human Rights said infighting among extremist militants operating in Syria had left around 3,300 casualties since January. Similar clashes claimed over 1,000 lives in January alone.
Syria has been gripped by deadly violence since March 2011. The West and its regional allies have been fuelling the unrest by providing militants with money and weapons.
According to some reports, the death toll from the three-year conflict exceeds 140,000 and a total of 7.8 million others have been displaced due to the violence.
HH/HH