Al Qaeda leader Ayman al-Zawahiri exhorted his fighters to find out who killed his chief representative in war-torn Syria , where militants have had a strong presence and strong rivalries amid the country 's civil war . Two suicide bombers in Aleppo killed Khaled al-Suri in February when they blew themselves up inside a compound used as a headquarters . Al-Zawahiri , in a recorded message posted on a militant website and uploaded on YouTube , deplored the action and called it `` sedition . '' `` All Muslims should not help those who blow up the headquarters of the holy fighters or those who send them car bombs and human bombs , and to stop supporting it in any way , '' the speaker said . CNN could not independently confirm that al-Zawahiri made the remarks . But his comments in the past have shown up on the same militant website . Syria , now in its fourth year of civil warfare , has been the site of what many have called a deadly proxy war between Shiite and Sunni militants . Iran has backed Bashar al-Assad 's government in Syria , and Hezbollah , the Lebanese Shiite group , has fought in support of the government . Sunni governments , such as Qatar and Saudi Arabia , have supported rebels . Islamic militants , such as al Qaeda-linked groups , have taken up arms in the country . Rivalry and fighting have emerged between extremist groups in Syria , such al Qaeda-linked Nusra Front and the Islamic State of Iraq and Syria . As a result , al-Zawahiri urged all Muslims and mujahedeen to refrain from infighting . `` Whoever commits such sins should remember that he is fulfilling for the enemies of Islam what they were unable to achieve on their own with all their resources , '' al-Zawahiri said . Well over 100,000 people have been killed and millions displaced in the civil war , the United Nations says . READ : Opinion : Forget Ukraine , Syria is now the world 's biggest threat .
Syria has been engulfed in civil war since March 2011 . Some see the conflict as a Sunni-Shiite proxy war . The al Qaeda leader emerged to deplore the killing of his top representative in Syria .