At least 1,069 people have died over the past two weeks in northern Syria in fighting pitting the Al Qaeda-linked Islamic State of Iraq and the Levant against rival rebel forces, activists said Thursday.

The Britain-based Syrian Observatory for Human Rights, which opposes Syrian President Bashar al-Assad, has kept track of the death toll since infighting among insurgents battling the Assad government began on Jan. 3, tallying up those killed in Aleppo, Idlib, Al-Raqqah, Deir ez-Zor, Homs and Hama provinces.

A total of 608 members of factions opposed to the Islamic State have died in the fighting, 113 of whom were executed by the jihadists.

At least 312 members of the Al Qaeda-linked group have died, 56 of them executed by rival combatants.

A total of 130 civilians also have died. Most of them perished in car-bomb attacks or in crossfire, although 21 were executed by the Islamic State, the Observatory said.

Those civilian fatalities also include an undetermined number of people who were executed by Islamic rebels for allegedly aiding and abetting the Al Qaeda-linked extremists.

The Observatory added that the bodies of 19 unidentified men were found inside the Islamic State's headquarters in the city of Aleppo after that stronghold was overrun last week by rival rebel forces.

On Jan. 3, rebels affiliated with the Islamic Front, the largest Islamic opposition alliance; the Free Syrian Army; and the Army of the Mujahedeen launched an offensive in several northern provinces to expel the Islamic State, which they accuse of abducting, torturing and killing those that oppose its ultraconservative interpretation of Islam.

Over the past week, the jihadists have recovered control of their main stronghold in the city of Al-Raqqah and seized nearly a score of towns outside Aleppo, although they were ejected from that major northern city on Jan. 8.

More than 120,000 people have died in Syria since March 2011, when Assad's brutal repression of pro-democracy protests ignited an armed conflict. EFE