42 fighters were reported killed Tuesday as ISIS forces moved into the Qalamoun mountains along the border between Syria and Lebanon, and fought rival rebel factions over the region.

The Qalamoun mountains have become a key rebel weapon smuggling route, as the simplest way to get arms into metro Damascus. This new ISIS interest may portend another push into the Yarmouk refugee camp.

The reports out of the region are that 12 ISIS fighters were killed, while 30 members of other rebel factions were also slain. Rebels have been fighting with Hezbollah and Syrian military forces for this territory for years.

Territory around Lebanon is particularly valuable because weapons and fighters are flowing both ways, with some factions establishing arms smuggling out of Lebanon, and groups like ISIS also trying to establish a presence in the border around the Lebanese town of Arsal, fighting with Lebanese military forces on a semi-regular basis.