The Syrian Democratic Forces (SDF) have advanced to within four kilometres north and east of al-Raqa city, AFP reported Tuesday (May 16th).

The advances bring the Arab-Kurd alliance closer than ever to the most important remaining Syrian stronghold of the "Islamic State of Iraq and Syria" (ISIS).

But the fighters are still 40 kilometres from al-Raqa to the west, and they do not control any territory directly to the city's south, which is bordered by the Euphrates river.

The SDF "on Monday took three villages four kilometres north of al-Raqa", spokesman Talal Sello said, adding that the alliance that night seized two more villages four kilometres to the east of the city.

"We are close to encircling al-Raqa from the east and the north, but we need to advance on the western front before launching the assault (on the city) at the right moment," he said.

ISIS fighters are still able to move in and out of the city via the area to its south, crossing the Euphrates by boat, according to SDF sources.

From there they head further south to the ISIS-held town of al-Sukhna in Homs province, and onwards east, to Deir Ezzor province, which remains mostly under the group's control.