The Kurdish-Syrian alliance battling to recapture Raqqa from ISIS has now seized about 45 percent of the militants' Syria stronghold, a top US official said Friday.

The US-backed Syrian Democratic Forces militia (SDF) began a campaign to capture Raqqa from ISIS last year, slowly encircling the city before breaking into it for the first time in June.

"As of today, the SDF has seized about 45 percent," of Raqqa, said Brett McGurk, the senior US envoy to the international coalition fighting ISIS in Iraq and Syria.

The recapture of Raqqa would mark a major milestone in the three-year effort to defeat ISIS.

The militants were ousted from their main Iraqi bastion of Mosul last month.

Still, the Raqqa battle is far from over, with thousands of ISIS militants remaining.

"I'm always hesitant to give numbers like that because this is an inexact science, but we think there's about 2,000 fighters left in Raqqa -- and they most likely will die in Raqqa," McGurk said.

The United Nations estimates between 20,000 to 50,000 civilians may still be in the city, though other estimates are lower.

source: AFP