Rebels clashed with an opposition unit linked to al-Qaeda in northern Syria, activists said yesterday, in a deadly battle that signals growing divisions among rebel groups and rising tensions between locals and more radical Islamist factions.

The rebel infighting comes as forces loyal to President Bashar al-Assad have made gains on the battlefield and drawn comfort from the downfall this week of Egypt’s Muslim Brotherhood, which under ousted President Mohamed Morsi had thrown its weight behind the Syrian opposition.

The Islamic State of Iraq and al-Sham (ISIS), the new al-Qaeda franchise announced by the head of global network’s Iraq leader, has been quickly working to cement power in rebel-held territories of northern Syria in recent months.

ISIS units have begun to impose stricter interpretations of Islamic law and have filmed themselves executing members of rival rebel groups whom they accuse of corruption, and beheading those they say are loyal to Assad.

Syria’s two-year revolt against four decades of Assad family rule has degenerated from a peaceful protest movement into a bloody civil war that has killed more than 100,000 people.

As fighting drags on and resources grow scarce, infighting has increased both among opposition groups and militias loyal to Assad, leaving civilians trapped in increasingly volatile and fragmented areas.

The latest internecine clashes happened in the town of al-Dana, near the Turkish border, on Friday, local activists said. The opposition group known as the Free Youths of Idlib said dozens of fighters were killed, wounded or imprisoned.