Some 3,300 people have been killed as a result of infighting between the rebel groups  seeking to overthrow Syrian President Bashar Assad since the start of 2014, the Syrian Observatory for Human Rights reported on Wednesday.
The Islamic State in Iraq and Greater Syria (ISIS), a small yet mighty offshoot of Al Qaeda, has been battling other rebel and insurgent groups across Syria, including the Al Qaeda-affiliated Nusra Front. 
The infighting between Syria's rebels began over power struggles and territorial disputes and has since whipped rebel-held territory into turmoil, Reuters reported.
The worst of the clashes between the rebel groups - and when the death toll initially began - broke out at the start of this year , according to Reuters.
In January, Al Qaeda chief Ayman al Zawahiri  called on all militants fighting in the Syrian civil war to unite. 
In a message posted online, the Al Qaeda leader called upon all jihadi factions taking part in the nearly three-year-old conflict to end the infighting  between the rebels.
"Our hearts are bleeding, the heart of our Islamic nation is bleeding when we see the internal strife among the mujahedeen in Syria," according to CNN.
Recent estimates suggest that more than 140,000 people have died  in the sprawling Syrian conflict. As of November 2013, an Oxford Research Group report indicated that 11,420 children had been killed since the crisis broke out, a number that has risen since the regime began indiscriminately targeting civilians through air raid and barrel bomb  campaigns across Syrian cities.