The Syrian Democratic Forces (SDF) on Thursday (June 29th) cut off the last escape route for the "Islamic State of Iraq and Syria" (ISIS) from al-Raqa, AFP reported.

The SDF captured two villages south of the Euphrates River that ISIS had been passing through to withdraw from the city, the Syrian Observatory for Human Rights said, and has been able to "completely encircle" al-Raqa.

SDF fighters have already captured two eastern and two western districts of the city and are pushing towards its centre, where ISIS is holding tens of thousands of civilians.

The SDF had surrounded the group from the north, east and west, but its fighters were still able to escape across the Euphrates, which forms the southern border of the city.

Thursday's advance saw SDF fighters capture the villages of Kasrat Afnan and Kasab on the southern riverbank, cutting off the route ISIS was using to withdraw to territory it controls in the Syrian desert and in Deir Ezzor province.

But dozens of ISIS fighters disguised in SDF uniforms launched a counterattack from the city centre, which they still control, on two districts in the city's south-east.

They carried out three suicide car bombings, deployed drones armed with explosives, seized six SDF positions and killed several fighters, Observatory head Rami Abdel Rahman said.