(Adds breakdown of death toll, background)
BEIRUT, Feb 26 (Reuters) - About 3,300 people have been killed in fighting between rebel factions trying to overthrow Syrian President Bashar al-Assad since the start of the year, the Syrian Observatory for Human Rights said on Wednesday.
The small but powerful al Qaeda-splinter group, the Islamic State in Iraq and the Levant (ISIL) has been caught up in clashes with other insurgents in Syria, including al Qaeda's official Syria branch, the Nusra Front.
The fighting started over power struggles and territorial disputes and has since spread throughout rebel-held territory in Syria.
The British-based Observatory said 924 ISIL fighters had been killed as well as 1395 militants from other rebel groups, which include the powerful Islamic Front alliance but also Western-backed rebel groups.
It added that around 700 more rebels from both sides were killed during clashes but were not claimed by the groups due to "extreme secrecy."
It said 281 civilians were also killed in the violence, the worse internecine fighting to break out during the nearly three-year revolt against Assad which has further divided an already fractured opposition
(Reporting by Oliver Holmes; Editing by Angus MacSwan)