Al-Qaida's leader has called on rival Islamic groups in Syria to end their infighting and focus their energies on battling against President Bashar Assad's forces.

The call by Ayman al-Zawahri came as activists say that fighting between the al-Qaida-linked Islamic State of Iraq and the Levant and an array of other Islamic militant groups has killed more than 1,000 over the past three weeks, mostly fighters on both sides.

Al-Zawahri says the internal fighting "has bloodied our hearts" and that it should stop immediately.

He called on Islamic groups in Syria to set up an Islamic court that would mediate and resolve their differences.

Al-Zawahri's five-minute audio message was posted online Thursday. Its authenticity could not be independently verified by it was posted on websites commonly used by militant groups.