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. ISIS has been accused of several human rights abuses, including torturing and murdering prisoners , among them children and teenagers, and forcing Druze men to convert to Islam or die . 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.