U.S.-backed SDF to announce operation in Syria's Deir al-Zor - SDF official

BEIRUT (Reuters) - U.S.-backed Syrian militias are set to announce an operation against Islamic State in the north of Deir al-Zor province, a senior SDF official told Reuters on Friday. The Syrian Democratic Forces (SDF) will formally declare the operation on Saturday, with the aim of pushing Islamic State back from northern parts of Deir al-Zor, the official said. They will launch the assault from the south of YPG-controlled Hasaka, the official said, part of a wider offensive to drive Islamic State out of Raqqa city and territory to its southeast. With U.S.-led air cover and special forces on the ground, the alliance of mostly Kurdish and Arab militias is fighting to seize Raqqa, upstream along the Euphrates River. Spearheaded by the Kurdish YPG militia, the SDF says it has taken 65 percent of Raqqa city from Islamic State. In the Deir al-Zor assault, the SDF would push toward the Euphrates River from the east of the province, which borders Iraq. The operation will likely bring the U.S.-backed militias into closer proximity with the Syrian military and allied forces, who have advanced on Deir al-Zor city. The Syrian army reached its enclave in Deir al-Zor city this week, on the western bank of the Euphrates, breaching an Islamic State siege that had lasted three years. With the help of Russian air power and Iran-backed militias, the advance capped months of steady progress east against Islamic State across the desert. The eastwards march has on occasion brought the Syrian army and its allies into conflict with U.S.-backed forces. Still, the rival campaigns have mostly stayed out of each other's way, and the U.S.-led coalition has stressed it is not seeking war with Damascus. (Reporting by John Davison; Writing by Ellen Francis; Editing by Hugh Lawson and Matthew Lewis)