US-backed Kurdish-led forces fighting Islamic State militants in Syria have said they are waging the "final" battle to uproot the extremists from Raqqa, once the terror group's de facto capital.
The battle could take hours or days, said Mustafa Bali, spokesman for the Kurdish-led Syrian Democratic Forces.
Losing the northern city of Raqqa, in many ways the symbol of IS' caliphate, would be yet another blow to the group and its reign of terror in the region as its strongholds crumble one after another in Iraq and other parts of Syria.
IS militants are desperately fighting in a number of neighbourhoods in the city, Mr Bali said.
"They are still able to fight but they will no longer determine the fate of the battle," he said.
"Our forces are waging the final phase of the battle of the presence of Daesh (the Arabic term for IS) in Raqqa. We have not decided if this battle will last hours, days or weeks."
Over the past days, mediation efforts by local tribesmen and the civilian council have secured the release of a number of civilians from Raqqa.
Council official Omar Alloush said 100 IS fighters surrendered to US-backed forces.
US officials have said only surrender, not a negotiated withdrawal for IS, would be accepted.
Hundreds of terrified civilians have been filmed fleeing towards the Syrian Democratic Forces from the last remaining neighbourhoods held by IS in Raqqa before the anticipated final battle between SDF and IS.
Earlier this week, US officials said an estimated 4,000 civilians were believed to be still trapped in the city.
A new video that emerged on Friday shows desperate, terrified residents emerging from destroyed districts, some of them collapsing on the ground in exhaustion as they arrive, in haunting scenes reflecting their years-old ordeal.
Militants seized Raqqa in 2014, the first city to fall under the full control of the extremist group.
It has since become synonymous with IS' rule of terror in the region, with civilians punished in public killings over the slightest perceived offence - videotaped killings that have shocked the rest of the world.
It was also from Raqqa, which became a destination for foreign fighters from around the world, that many of IS attacks in the West were plotted.
The latest battle for Raqqa began in June, with heavy street-by-street fighting amid intense US-led coalition air strikes and shelling.
The battle has dragged on in the face of stiff resistance from the militants and civilians trapped in the city.
On Saturday, the SDF said it seized the al-Nahda neighbourhood in Raqqa's western sector.
A day earlier, IS carried out an offensive on SDF forces near the city's main hospital, an IS fortified headquarters.
The Syrian Observatory for Human Rights, a British-based monitoring group with activists on the ground, said negotiations over the fate of foreign fighters who remained in Raqqa had delayed the final push to regain control of the city.
SDF officials deny there are talks to evacuate IS fighters.