BEIRUT (AP) — A U.S.-backed Syrian force says it has launched military operations against the Islamic State group in eastern Syria, heightening the possibility of conflict with rival, Russian-backed government forces, which are running their own operations in the same area.

The predominantly Kurdish Syrian Democratic Forces announced Saturday its Deir el-Zour Military Council has launched operation "Jazeera Storm" to defeat IS militants in the resource-rich Deir el-Zour province.

Syrian government forces broke an IS siege against the provincial capital, also called Deir el-Zour, last week.

The...