Some 3,300 people have been killed in fighting between rebels seeking President Bashar al-Assad's ouster and their erstwhile jihadist allies since clashes erupted in January, a monitoring group said Wednesday.
"Some 3,300 people have been killed ever since the start of fighting on January 3 between the (jihadist) Islamic State of Iraq and the Levant (ISIL) on one side, and (rebel) Islamist and other groups on the other," said the Syrian Observatory for Human Rights.
The deaths came "in car and (other) bomb attacks, suicide blasts and fighting," said the Britain-based Observatory, which relies on activists and other sources inside Syria.
While rebels initially welcomed ISIL in their battle to overthrow Assad, many of them later turned against the group, accusing it of hijacking the rebellion and carrying out a string of kidnappings and killings of activists and rival rebels.
Among the overall fatalities were at least 281 civilians, the majority of them killed by shelling and stray bullets, the Observatory said.
But 21 of them were executed in a children's hospital-turned-ISIL prison in the northern city of Aleppo, it said.
And it said the jihadists executed a family of seven Kurds, beheading some of them, at a prison in the Aleppo countryside.
Most of the dead were fighters from both sides.
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The Observatory has documented the deaths of 924 ISIL members and 1,380 rebels, including Islamists.
It also said more than 700 other fighters from both sides had died in battle but could not be identified, while 29 bodies were found in ISIL bases, most likely executed by the jihadists expulsion before their expulsion.
ISIL first appeared in Syria in late spring 2013, but it was not until early January that rival rebels declared war against it.
ISIL has entered into battle against moderates, Islamists and even rival jihadists from Al-Nusra Front, the official arm of Al-Qaeda in Syria.
On Tuesday, Al-Nusra Front gave ISIL a five-day ultimatum to submit to a joint Islamic court after a top operative was killed in a suicide bombing.
Rival rebels accuse ISIL of being behind the fatal attack and Al-Nusra's chief said his outfit would fight the group in Syria and neighbouring Iraq if it refused joint arbitration.
Since January, ISIL has been driven from many areas where it previously had positions.
But Romain Caillet, a researcher on Islamist movements, said it retains control of Raqa, Tal Abyad, Jarablus, Minbej, Azaz, several towns in Hasake province and two villages in Deir Ezzor province.
Raqa is the only provincial capital lost by the regime since the start of the conflict nearly three years ago.
Tal Abyad, Jarablus, Minbej and Azaz are strategic for their location on Syria's long border with Turkey.