BEIRUT (AP) — A Syrian rebel group named a new leader and military chief on Wednesday, less than 24 hours after an explosion killed nearly a dozen of its senior figures in a devastating blow to one of the most powerful factions in the country’s armed opposition.

The group, Ahrar al-Sham, has been among the steadiest and most effective forces fighting to oust President Bashar Assad in Syria’s civil war. It has also been on the front lines of a now nine-month battle in northern Syria against the extremist Islamic State group.