Advancing Kurdish and Arab fighters backed by US-led air strikes now control 40 percent of the Islamic State stronghold of Manbij in northern Syria, a monitor said Sunday.

The Syrian Observatory for Human Rights said the Syrian Democratic Forces (SDF) had pushed deeper into the town near the border with Turkey, with air cover from the US-led coalition against the jihadists.

Around 2,300 civilians have fled Manbij in the past 24 hours as the SDF fighters advanced, according to the Britain-based monitor.

"It's a street battle, and the process of eating away at IS territory is ongoing," Observatory director Rami Abdel Rahman told AFP.

(AFP)