The Syrian Democratic Forces (SDF) say they are nearing the "final week" of their assault to drive the "Islamic State of Iraq and Syria" (ISIS) from its one-time Syrian bastion al-Raqa, as the group's self-described caliphate crumbles.

Losing al-Raqa would be only the latest in a series of crushing defeats for the extremist group, which once controlled large swathes of territory spanning the border between Syria and Iraq.

The SDF have captured around 90% of al-Raqa since entering the city in June, after months of fighting to encircle it.

The alliance of Kurdish and Arab fighters is now advancing on ISIS-held districts from two fronts in the city's north and east, commander Rojda Felat, who heads the "Wrath of the Euphrates" campaign, said Sunday (October 8th).

She said fighting was still fierce along the front line, with ISIS using snipers, suicide bombers and reinforced positions in tunnels to hold up the SDF advance.

Handful of positions left

The extremist fighters still hold al-Raqa's national hospital, the nearby football stadium and surrounding residential neighbourhoods, including the infamous al-Naim roundabout, where ISIS staged public beheadings and crucifixions.

"There were intermittent clashes today around the hospital and the stadium," the head of the SDF's press centre Mustafa Bali said Monday.

"There was no notable or tangible advance, but shelling and sniping operations are ongoing."

SDF fighters have surrounded the hospital ahead of a push to seize al-Naim, said Ali Sher, a field commander with the Kurdish People's Protection Units (YPG).

ISIS is believed to be holding civilians as human shields in the hospital, complicating efforts to capture the position.

Col. Ryan Dillon, spokesman for the international coalition backing the SDF's assault, said ISIS was using the hospital as a military base and it was "heavily fortified".