In the meantime, Alloush appeared in a 15-minute video on YouTube Wednesday, exhorting his men against ISIL, which this week declared a caliphate in parts of Iraq and Syria, led by Abu Bakr al-Baghdadi.

Alloush called the group “khawarij.” “This group of khawarij, the gang of [Abu Bakr] al-Baghdadi ... tried to destroy jihad in Afghanistan, in Chechnya, in Bosnia-Herzegovina and in Iraq. They have now come to try and destroy jihad in Syria,” he tells dozens of assembled fighters in the video.

In the meantime, Alloush relates several instances of atrocities committed by ISIL militants in recent months, including the murder of a leading terrorists commander, known as Abul-Miqdam. “They forced him to the ground and slit his throat,” Alloush said, referring to the widely reported incident from last month.

Alloush said he and his comrades in the north had intercepted walkie-talkie conversations between ISIL militants, many of them non-Syrians, which demonstrated their ruthlessness and often utter disregard for civilians they encountered. “They are dirty bastards, with an evil ideology,” Alloush said.

On Tuesday, fighters from Jaish Al-Islam ejected ISIL from the Ghouta town of Midaa after three days of heavy clashes, according to pro-opposition media reports.