Al-Qaeda 's leader called on fighters to determine who killed his chief representative in Syria, a man many militant groups believe died at the hands of a rival militia, in a move that highlighted a conflict between rebels that has killed hundreds.
In a thinly veiled criticism of the breakaway Islamic State in Iraq and the Levant organization, Ayman al-Zawahri called the killing of Abu Khaled al-Suri an act of "sedition" that should be handled in accordance with Islamic law.
"All Muslims should not help anybody who blows up the headquarters of the holy fighters, or who sends them car bombs and human bombs," he said in a recorded message posted on militant websites late Friday, referring to the Islamic State's tactic of attacking rival rebels with bombings.
"Whoever commits such sins, should remember that he is fulfilling for the enemies of Islam what they were unable to achieve on their own."
Al-Suri was killed on Feb. 23, when two suicide bombers blew themselves up inside the militant leader's compound in the northern Syrian city of Aleppo.
While he did not mention the Islamic State by name, it was clear he was accusing the group and staking out a hard stance against it. He also endorsed a previous call for Islamic arbitration over the death of al-Suri, to be overseen by the Nusra Front — the official Al-Qaeda affiliate in Syria.
Al-Suri was the founder of a conservative, powerful Syrian rebel group, Ahrar al-Sham.
The Islamic State, led by man known as Abu Baker al-Baghdadi, was once an al-Qaeda-affiliated group that operated in Iraq, but also branched into Syria.
It was expelled from the militant franchise in part because of brutality that included public beheadings — considered excessive even by the standards of Al-Qaeda 's ultraconservative Muslim fighters. Al-Qaeda formalized the expulsion last week.
The shadowy Al-Baghdadi is one of the world's most lethal terrorists, infamous for his relentless bombing campaigns against Iraqi civilians, audacious jailbreaks of fellow militants and for expanding the organization into Syria.
Zawahri's message also suggested that rebels will remain locked in the infighting that has eroded their ranks and cost them territory to government forces supporting President Bashar Assad.
Infighting has killed at least 3,000 rebels since January according to a count by the British-based Syrian Observatory for Human Rights.
Syria's uprising, which began with largely peaceful protests in March 2011, has evolved into a civil war with sectarian overtones. Islamic extremists, including foreign fighters and Syrian rebels who have taken up hard-line Al-Qaeda -style ideologies, have played an increasingly prominent role among fighters, dampening the West's support for the rebellion to overthrow Assad.