Al Qaeda chief Zawahri tells Islamists in Syria to unite.

Al Qaeda chief Zawahri tells Islamists in Syria to unite.(Taz).

Al Qaeda leader Ayman al-Zawahri called on militant rebel factions in Syria to stop fighting each other and set up a judicial committee to sort out their differences, according to an audio recording released on Islamist websites, Reuters reported.

The small but powerful al Qaeda-linked Islamic State in Iraq and the Levant (ISIL) has been caught up in clashes with other Islamist insurgents in recent weeks, often triggered by disputes over authority and territory.

"Our hearts and the hearts of the (Muslim) nation, which hangs its hopes on you, have bled for the infighting that has spread between the ranks of those waging jihad for Islam," Zawahri said in the five-minute recording.

"We call on all our brothers in all the jihadist groups ... to work towards ending this sedition, which will lead to only God knows what," Zawahri said.

Reuters was unable independently to confirm the authenticity of the recording, but the voice bore a clear resemblance to that of Zawahri.

The insurgent groups fighting ISIL range from relatively secular moderates to Islamists, including the al Qaeda-aligned Jabhat al-Nusra, in the worst rebel-on-rebel violence since Syria's conflict began in March 2011.

In April, the head of ISIL, Abu Bakr al-Baghdadi tried to merge ISIL with Jabhat al-Nusra, defying orders from Zawahri and causing a rift.

The fighting since the start of January has killed more than 1,000 people, according to Syrian Observatory for Human Rights monitors. The fissures within rebel ranks have helped President Bashar al-Assad's forces claw back territory around the northern commercial hub of Aleppo.