CAIRO - Al-Qaida'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," al-Zawahri 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-Qaida affiliate in Syria.
Al-Suri was the founder of a conservative, powerful Syrian rebel group, Ahrar al-Sham.
The Islamic State, led by a 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-Qaida's ultraconservative Muslim fighters. Al-Qaida formalized the expulsion last week.
The shadowy Al-Baghdadi is one of the world's most feared 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. That fighting has killed at least 3,000 rebels since January, according to a count by the British-based Syrian Observatory for Human Rights.
The message came as mortar shells continued to hit the Syrian capital and the central city of Homs amid heavy fighting Saturday in the suburbs of the Damascus, activists and state media said.
State news agency SANA said two mortar shells struck the Opera House in central Damascus without causing any casualties. It said 17 mortar shells struck the Damascus suburb of Jaramana, a government stronghold, wounding 13 people.
It was not clear if the Opera House was targeted in the shelling or was hit randomly. Assad gave a defiant speech there last year vowing to keep fighting.
In Homs, a rocket struck a market in the western neighborhood of Inshaat, killing six people and wounding, SANA said. The market is about 500 meters (yards) from the Safir Hotel that is used by the United Nations in the city.