At least 482 people have been killed in fighting between the Al-Qaeda-linked Syrian rebel group Islamist State in Iraq and the Levant (ISIS) and other Syrian rebels, the Syrian Observatory for Human Rights has reported.
Eighty-five civilians were among the dead, along with at least 240 non-ISIS rebels and 157 ISIS members.
The high death toll was reported after just one week of fighting across various provinces of northern Syria. Three powerful rebel alliances – among them Islamist groups - have teamed up to fight ISIS, which they have warned is worse than the Bashar Assad regime.
The Al-Qaeda linked group has vowed to “crush” other rebel groups in Syria.
Rebels with the Islamic Front have made gains against ISIS, capturing a key base in Aleppo and advancing in the Idlib province. However, they have reportedly been struggling to oust ISIS in its stronghold of Raqqa.