Syrian Democratic Forces (SDF) fighters dance in the north of Raqqa city, Syria February 3, 2017.

A US-backed alliance of Syrian Kurdish and Arab fighters took full control Sunday of the Tabqa military airport in the country’s north from ISIS, a spokesman said.

The advance comes as the Syrian Democratic Forces alliance prepares for an assault on the militant group’s de facto Syrian capital Raqqa, some 55 kilometers (35 miles) east of Tabqa.

The SDF is seeking to effectively encircle Raqqa city before attacking the stronghold.

“The Syrian Democratic Forces have full control of Tabqa military airport and operations to clear and demine are under way in order to secure the airport fully,” spokesman Talal Sello told AFP.

The SDF entered the airport earlier Sunday, with Sello saying the alliance’s forces were engaged in fierce clashes with ISIS.

The Syrian Observatory for Human Rights monitor, which also confirmed the airport’s capture, said the SDF fighters were backed by US-led coalition strikes.

US forces airlifted SDF fighters behind ISIS lines around Tabqa earlier this week in advance of the assault, which is also targeting the town of Tabqa and the nearby Tabqa dam, Syria’s largest.