The U.S.-backed Syrian Democratic Forces said Wednesday that its fighters are besieging the Islamic State militants inside the city of Raqqa in northeastern Syria.

In a short statement on its official Twitter account, the SDF, an alliance of Kurdish, Arab and Assyrian fighters led by the Kurdish YPG group, said IS militants are besieged in the “last few areas they are still holding in Raqqa.”

It added that the Syrian militants of IS are surrendering themselves, while the foreigners are withdrawing toward the eastern province of Deir al-Zour.

Recently, the Syrian Observatory for Human Rights monitor group said the SDF had become in control of 55 percent of Raqqa city, following a two-month offensive.

The U.S.-led aircraft are also heavily backing the SDF in their push to strip IS of their main stronghold in Syria.