Powerful rebel groups in Syria, including the Islamic Front and Al-Qaeda's affiliate Al-Nusra Front, have been locked in fierce fighting with the Islamic State of Iraq and the Levant (ISIL) since January.
The fighting broke out after allegations that ISIL brutally abused civilians and other opposition fighters battling to topple the regime of Syrian President Bashar al-Assad.
Tensions were further exacerbated when Al-Nusra and other rebel factions accused ISIL of killing Islamist Front commander Abu Khaled al-Suri in a suicide car bomb attack in February.
Zawahiri eulogised him in the audio statement posted on the Internet by jihadist groups, saying his death was the result of "sedition" under way in Syria.
He called on "every Muslim and mujahid (jihadist)" to confront sedition and "accept independent sharia arbitration", or the ruling of an Islamic court, to end rebel infighting in Syria.
Jihadists "must disavow anyone who refuses (such) arbitration" and should not take part in the killing of fellow Islamist fighters, he added.
