Al-Qaeda's command has cemented its split with its one-time Iraqi affiliate, in a statement distancing itself from the Islamic State of Iraq and the Levant and its battle with Syria's rebels.
The statement released late Sunday builds on previous comments by Al-Qaeda chief Ayman al-Zawahiri, who has called on ISIL to withdraw from Syria and deemed another jihadist group, the Al-Nusra Front, Al-Qaeda's official Syrian affiliate.
The statement comes as moderate and Islamist Syrian rebels are locked in brutal conflict with ISIL.
The clashes began in early January, after accusations that ISIL was abusing both civilians and rival rebel forces. The fighting has left more than 1,700 people dead, according to a monitoring group.
"Al-Qaeda announces it is not linked to the Islamic State of Iraq and the Levant, as it was not informed of its creation... (and) did not accept it," the statement said.
ISIL "is not a branch of Al-Qaeda, has no links to it, and the (Al-Qaeda) group is not responsible for its acts," it added.
ISIL grew from the Islamic State of Iraq, Al-Qaeda's one-time Iraqi affiliate, led by Abu Bakr al-Baghdadi.
In the early days of the Syrian conflict, which began in March 2011, ISIL dispatched members to the country to start forming a fighting force.
Shortly afterwards, Al-Nusra Front emerged and began claiming responsibility for attacks against the regime.
In April 2013, Baghdadi announced his group would merge with Al-Nusra to form the Islamic State of Iraq and the Levant, but they rejected his overtures and pledged direct allegiance to Zawahiri.
The Al-Qaeda chief also rejected the merger, ordering ISIL to return to Iraq, a directive they ignored.
Charles Lister, a visiting fellow at the Brookings Doha Centre, said the new statement was unlikely to chasten ISIL.
"Considering its long-established behavioural norms, it seems unlikely that ISIL will issue anything representing an apology or retraction," he said.
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"All of this is damaging to the Syrian revolution," he added.
"So long as it continues, these inter-group hostilities make any kind of provincial, let alone national, opposition victory in Syria highly unlikely."
The statement comes as a bloody conflict-within-a-conflict between ISIL and other rebels plays out in opposition areas of Syria.
Al-Nusra has largely remained out of the fighting, with its chief calling for a truce, though its forces have battled ISIL in limited areas.
Some rebels initially welcomed jihadists to the fight in Syria, valuing their battlefield experience, funding and weapons.
But ISIL has drawn the ire of many for imposing harsh Islamic strictures, including bans on music and smoking, detaining and torturing rebels and civilians, and seeking to consolidate its power in areas under its control.
Al-Qaeda's statement criticised ISIL's tactics, saying jihadists should "be part of the nation" and avoid "any action that could lead to the oppression of jihadists, Muslims or non-Muslims."
Jihadists must "not rush to announce emirates and states... and impose them on people," it added.
In a new toll on Monday, the Syrian Observatory for Human Rights said at least 1,747 people had been killed in the clashes since January 3, including 215 civilians.
At least 979 moderate and Islamist rebels were killed in the fighting, along with 531 ISIL members, the group said, adding that the real toll was likely to be much higher.
Aron Lund, editor of the Carnegie Endowment's Syria in Crisis website and an expert on the conflict, said the statement could open cracks within ISIL.
He noted that the statement followed comments from a prominent Salafist Saudi cleric who publicly criticised ISIL for failing to sign up to a jihadist "peace plan".
"It's quite possible that (it) could cause splits in the Islamic State. And even if it doesn't, it's likely to hurt their ability to recruit and pull in financing," he said.
But the pressure was unlikely to prompt ISIL to shift course, he said.
"If history is anything to go by, the Islamic State will respond negatively. They always do, they never compromise."