BEIRUT (Reuters) - U.S.-backed forces trying to oust Islamic State militants from the Syrian city of Manbij took "almost complete control" of the city on Saturday, the Syrian Observatory for Human Rights said.

The Syria Democratic Forces (SDF), which includes the powerful Kurdish YPG militia and Arab fighters, launched its campaign two months ago with the backing of U.S. special forces to drive Islamic State from a last stretch of the Syrian-Turkish frontier.

The official spokesman of the SDF-allied Manbij military council, Sharfan Darwish, told Reuters that battles were continuing but that around 90 percent of the city had now been cleared of the ultra hardline Sunni militants .

Pockets of militants are still present in the center of the city, the Britain-based Observatory said.

A spokesman for the U.S. coalition against Islamic State told Reuters there had been "continued progress" in Manbij, and the coalition would continue to support the SDF for as long as the operation took.

Manbij is in the northern province of Aleppo, which forms a theater for several separate battles between multiple warring sides in Syria's five-year-old conflict.

(Reporting by Lisa Barrington; Editing by Ralph Boulton)