Update | Syrian rebels join forces against al-Qaeda-linked ISIL

Syrian rebels have united to kill and capture dozens of jihadists in a new "revolution" against the al-Qaeda-affiliated Islamic State of Iraq and the Levant, whom they accuse of carrying out worse abuses than those of President Bashar al-Assad.

Three powerful rebel alliances have taken on ISIL during two days of fierce combat in Aleppo and Idlib provinces that Syria's main opposition National Coalition said it "fully supports".

The reports come a second day into clashes in opposition areas of the northern and northwestern provinces between ISIL and rebel alliances, which include the Islamic Front and the Syrian Revolutionaries Front.

Jihadists who flocked to Syria to join the rebels in their fight against Assad were at first welcomed by the armed opposition.

But relations grew bitter after ISIL fought other opposition groups for control and committed systematic abuses against activists and rival rebels, as well as ordinary citizens.

"This is more important than fighting the regime," said Mohammed Azzouz, an anti-government activist from the eastern city of Raqqah who was forced into exile in Turkey by the extremists late last year.