US support Syrian rebel-Kurdish assault on IS-held dam
Members of the Syrian Arab Coalition, part of the Syrian Democratic Forces [SDF], were airlifted in a bid to retake the Tabqa dam near the Islamic State group stronghold.
"Coalition forces are assisting the Syrian Arab Coalition with airlift and fire support in an operation to seize the Tabqa dam," Pentagon spokesman Major Adrian Rankine-Galloway said.
He did not provide details on the number of fighters moved.
Raqqa 24 monitoring site reported that IS had evacuated civilians from the area, while five US-led coalition fighter jets were patrolling overhead to prevent militants escaping.
SDF forces were reported to be crossing Lake Assad in boats, while troops and armour were being rushed to the area recently taken by anti-IS forces.
A US defence official also confirmed artillery is being used in the operation, according to AFP.
The Tabqa Dam provides electric power to large parts of Syria, according to the US, but the area has been under Islamic State group control since 2013.
Capturing the dam is an important step in the isolation of the area around Raqqa, in preparation for an offensive to eventually retake the city from IS control.
The fall of Raqqa would be a massive blow for IS, while an ongoing assault by Iraqi forces on the group's other main city, Mosul, is also depleting its manpower.