Eighteen fighters were killed in a car bomb blast that hit a Syrian insurgent group in the southern province of Quneitra on Wednesday, monitors reported, and a rebel source said the attack was likely carried out by hardline Islamists.

The Syrian Observatory for Human Rights monitoring group said the explosion occurred in the village of al-Isha, targeting a base belonging to Jabhat Thuwwar Souria, a Free Syrian Army group.

Issam al-Rayyes, spokesman for the Southern Front of the Free Syrian Army, said 11 people had been killed in the blast, including the Front's commander, known as Abu Hamza al-Naimi.

Rayyes said it was not clear who was behind the attack.

Suhaib al-Ruhail, a spokesman for the Alwiyat al-Furqan group which operates in the area, said it was most likely carried out by "Daesh sleeper cells", a reference to Islamic State insurgents. He gave a lower initial death toll of 10 people.

The incident did not immediately appear to be related to the current cessation of hostilities between the Syrian government and its allies and non-jihadist insurgent groups.

(Reporting by John Davison in Beirut and Suleiman Al-Khalidi in Amman; Editing by Mark Heinrich)

REUTERS