ISTANBUL, Turkey — Al-Qaida's central leadership has officially cut ties with a powerful jihadist group that has flourished in the chaos of the civil war in Syria and that rushed to build an Islamic state on its own terms, antagonizing the wider rebel movement.
The animosity between the group, the Islamic State of Iraq and the Levant, or ISIL, and other rebel groups has fueled the deadliest infighting between the foes of President Bashar Assad and sapped their campaign to depose him.
Though isolation of the group could lead to greater unity among other rebel forces, it is unlikely to assuage fears in the United States and elsewhere about the increasing power of extremists in Syria.
The break between al-Qaida and ISIL, announced late Sunday, served both sides, said William McCants, a scholar of militant Islam at the Brookings Institution, a think tank based in Washington. Al-Qaida cut ties with a group that was besmirching al-Qaida's name among other militants, while ISIL, also known as the Islamic State in Iraq and Syria, or ISIS, bolstered its image as a force to reckon with, he said.
"ISIS is now officially the biggest and baddest global jihadi group on the planet," McCants said. "Nothing says 'hard core' like being cast out by al-Qaida."
ISIL's haste to seize resources like oil fields and border crossings brought it into conflict with other rebels, and widespread clashes between the sides in recent weeks have left thousands dead across northern and eastern Syria, according to partisan activist groups.
In a written statement posted on jihadist forums, al-Qaida accused ISIL of not working with other groups, naming its own leaders and trying to impose its own authority.