Al-Qaeda chief Ayman al-Zawahiri has called for Islamist fighters in Syria to end the infighting that killed a one-time companion of Osama bin Laden earlier this year, according to an audio tape posted online.
In the message, Zawahiri mourned the death of Abu Khaled al-Soury, who was killed by an al Qaeda splinter group in a suicide attack in February, and lamented the "strife of the blind that has befallen the blessed land of the Levant."
Soury was one of the highest-profile victims of rebel infighting that surged at the start of the year, pitting the Islamic State of Iraq and the Levant (ISIL) against rival rebels including other hardline Islamists.
Some 4,000 people have been killed in the clashes, according to the Britain-based Syrian Observatory for Human Rights.
The fighting has hindered the battle against President Bashar al-Assad and pushed rival rebel groups to consolidate power in their respective areas of control.
"Today this strife requires that all Muslims stand up against it and form a general view against it and against all who do not accept the independent sharia arbitration," Zawahiri said in the audio message, referring to Islamic law.
Reuters could not verify the authenticity of the Zawahiri tape, which was posted on Friday, but the voice resembled that of the al Qaeda leader.
Al Qaeda said it was breaking with ISIL in February after disputes over the group's refusal to limit itself to fighting in Iraq rather than in Syria, where the Nusra Front is al Qaeda's affiliate.
The Nusra Front and ISIL have occasionally clashed since the infighting erupted in January, but they have also fought side by side in some areas and the Nusra Front has tried to mediate between ISIL and rival rebels in others.
ISIL is a rebranding of al Qaeda in Iraq, which fought against American forces during the U.S. occupation. It draws strength from a core of foreign fighters and has imposed a strict interpretation of Islamic law in territories it controls.
In the audio tape, Zawahiri recalled knowing Soury since the days of the fight against Soviet Union forces in Afghanistan in the 1980s, and called for Islamist fighters to reject the infighting in Syria.
"Everyone who has fallen into these sins must remember that they accomplish for the enemies of Islam what they could not accomplish by their own abilities," he said.
Soury was born in Syria's northern city of Aleppo in 1963. He was believed to have fought in Afghanistan and Iraq and was more recently a commander in the Syrian Islamist rebel group Ahrar al-Sham.
Although he did not specifically refer to ISIL, Zawahiri said Soury had seen echoes of past Islamist infighting in the clashes in Syria. "This sedition which Abu Khaled witnessed and warned of, God willed that it make him a martyr," he said.
(Additional reporting by Mostafa Hashem in Cairo; Editing by Sami Aboudi and David Holmes)