Extremist groups in Syria, including the so-called "Islamic Front" and Al-Qaeda 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 insurgents battling in Syria.

Tensions were further exacerbated when Al-Nusra and other terrorist factions accused ISIL of killing "Islamic Front" commander Abu Khaled al-Suri in a suicide car bomb attack in February.

Abu Khaled was reportedly appointed last year as Zawahiri's representative in Syria and was once close to former Al-Qaeda ringleader Osama bin Laden.

Zawahiri eulogized him in the audio statement posted on the Internet by extremist groups, saying his death was the result of "sedition" under way in Syria.

He called on the extremist insurgents to confront sedition and accept independent arbitration, or the ruling of a court, to end militant infighting in Syria, AFP reported.

Militants "must disavow anyone who refuses (such) arbitration" and should not take part in the killing of fellow extremists, he added.

Al-Nusra Front chief Abu Mohammed al-Jolani has accused ISIL of murdering Abu Khaled and warned the group he would fight it inside Syria and Iraq, where ISIL has its base, unless it accepts the arbitration.

Zawahiri called on the extremists to stop the infighting when clashes first erupted in January.

This is the second time that he has called for an end to militant infighting. In late January, Zawahiri issued a similar message.

NTJ/MB