A car bomb that struck an insurgent group left 18 fighters dead in Syria's southern province of Quneitra on Wednesday, according to an activist group and reports by Reuters.
A rebel source said the attack was likely carried out by Daesh or a similar extremist militant group.
The Britain-based Syrian Observatory for Human Rights told Reuters the explosion took place in the village of al-Isha, striking a base belonging to a Free Syrian Army group, Thuwwar Souria.
Suhaib al-Ruhail, a spokesman for the Furqan Brigade, said it was most likely carried out by "Daesh sleeper cells."
The attack did not seem to be a breach of the current ceasefire between the Syrian government and various "moderate" rebel groups.
