In the northern city of Aleppo, Syria’s largest, 44 fighters were killed in three days of clashes between the Islamic State of Iraq and the Levant (ISIL) and a rival group formerly known as Ghurabaa al-Sham.
The Observatory said 14 of the dead belonged to ISIL, which was able to control three neighborhoods in Aleppo.
Rebel groups have become increasingly fractured, with Islamic extremists assuming prominent roles in battle.
In an audio message on Friday, the leader of al-Qaeda urged jihadis in Syria to unite, an appeal likely aimed at rival affiliates of his terror network operating in the country.
Ayman al-Zawahri said fighters must “rise above organizational loyalties and party partisanship” and unite behind the goal of setting up an Islamic state.
He suggested he will not impose unity, saying that “what you agree upon will also be our choice.”
Two al-Qaeda-linked groups have emerged — Jabhat al-Nusra and ISIL. The first is commanded by a Syrian, the second by an Iraqi, but both are believed to be loyal to al-Zawahri.
Al-Zawahri also urged Syrian regime opponents not to cut deals with Western powers and secular groups.