Abu-Abdallah al-Libi, a top commander with the Al-Qaeda linked group The Islamic State of Iraq and Greater Syria (ISIS) was killed on Sunday in Idlib in northwestern Syria, Al Arabiya television reported.
The Free Syrian Army denied responsibility for Libi’s death.
The militant group is posing growing challenges for the armed opposition fighting to overthrow Syrian President Bashar Assad and aspire to build a democratic civilian system in the country.
This week the extremist group took control of the Syrian town of Azaz, on the border with Turkey.
Syrian Youth activists had launched an online campaign entitled “ISIS doesn't represent me.”
“I hope Azaz turns into ISIS' burial ground,” said one activist posting on Twitter, according to AFP.
“They failed against the Americans in Afghanistan, and against the Iranians in Iraq. Now they are here to bully the Syrians, who are fighting a criminal regime,” said another.
An online activist said he feared ISIS would try to impose Islamic law in Azaz.
“Sharia law would only be imposed to allow the killing of people, and we don't want that,” he said.
Another activist echoed a common claim that ISIS is working hand in glove with Assad's regime, and was mirroring its methods by “attacking field hospitals, detaining doctors and killing activists.”
Activists said the battle for Azaz began when jihadists broke into a field hospital, searching for a German doctor.
Another version of Wednesday's events says the fighting broke out when a Northern Storm rebel stepped in to defend a German journalist from being kidnapped by ISIS.
The FSA regained control of the town after heavy clashes. The Syrian Observatory for Human Rights reported Azaz was calm by Thursday, Al Arabiya television reported.
Translated and edited by The Syrian Observer