Ahrar al-Sham is a militants group and part of the Islamic Front alliance that has been in armed conflict with ISIL terrorist group which has seized swathes of territory in Syria and Iraq.

A Tuesday statement posted on Ahrar al-Sham's official Twitter feed said the blast had hit a meeting in Idlib province in northwest Syria and confirmed Hassan Aboud, the group's leader, among at least 12 dead.

"We don't know the cause of the explosion yet," Abu Mustafa al-Absi, a member of Ahrar al-Sham's politburo told Al-Jazeera TV in an interview.

"We do not rule out the infiltration of elements who were able to plant a bomb," he added.

The so-called Syrian Observatory for Human Rights, the monitoring group, said some 50 of the group's leaders had been gathered at a house when the blast went off. Rami Abdulrahman, who runs the Observatory, said the blast had occurred inside the meeting.

Ahrar al-Sham is widely believed to have received funding from Persian Gulf states. It was at one point considered the strongest insurgent group in the Syrian civil war.

Syrian state TV flashed an urgent news headline reporting Aboud's death.

In January another senior Ahrar al-Sham leader, Abu Khaled al-Soury, was killed in a suicide attack. Soury had fought alongside al-Qaeda founder Osama bin Laden and was close to its current chief Ayman al-Zawahri.

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