Al-Qaeda's leader ordered the group's Syrian affiliate, the al-Nusra Front, to end fighting with jihadist rivals, in an audiotape published online Friday.

Ayman al-Zawahiri, in a message to Al-Nusra chief Abu Mohammed al-Jolani, ordered that "all soldiers of the front immediately cease fighting" other jihadist groups.

Powerful rebel groups in Syria, including al-Nusra Front, have been locked in fierce fighting with the Islamic State of Iraq and the Levant since January that has killed thousands of fighters.

ISIL was initially welcomed by other rebels, who have been fighting to topple Syrian President Bashar Assad since 2011, but allegations of brutal abuses against civilians as well as rival opposition fighters sparked a backlash.