US-backed forces drive ISIS out of Raqqa in major victory

US-backed forces took full control of Raqqa in Syria from the Islamic State group on Tuesday, defeating the last militant holdouts in what had become the virtual capital of the now-shattered "caliphate".

Declaring victory, the US-backed militias raised flags over Raqqa after a four-month battle. The Sunni militant group often referred to as ISIS overran Raqqa in January 2014, seizing control from rebel factions opposed to the rule of Syrian President Bashar al-Assad.

The victory hammers another nail in the coffin of the jihadist group's experiment in statehood, which has collapsed in the face of offensives in Syria and Iraq.

Inside Raqqa, overjoyed fighters from the Kurdish-Arab Syrian Democratic Forces celebrated and raised their yellow flag in the city's Al-Naim traffic circle, which became known as "Hell Roundabout" after jihadists used it for gruesome public executions.

Raqqa had become a byword for atrocities carried out by the jihadists and it was from the city that Islamic State organised devastating overseas attacks like the Paris massacres in 2015 or the August attacks in Barcelona.

"Hell Roundabout is now Al-Naim Roundabout again," the fighters in Raqqa cheered, surrounded by crushed buildings and charred cars damaged in the fierce battle for the city.

Rojda Felat, the SDF's commander for its Raqqa operation, flashed a wide grin as she waved a huge yellow flag emblazoned with the militia's name, her rifle hanging from her shoulder, AFP reports.

The defeat of Islamic State in Raqqa was a victory "the whole world was waiting for," said Omar Alloush, a member of the Raqqa Civil Council formed to run the city after its liberation.

Raqqa has been devastated by fighting and emptied of civilians, with the last few thousand departing under a deal implemented over the weekend.

SDF forces broke into Raqqa in June after months of fighting to surround the city. On Tuesday they flushed the last few hundred IS fighters from their remaining positions in the main hospital and the municipal stadium.

"Everything is finished in Raqqa, our forces have taken full control of Raqqa," the alliance's spokesman Talal Sello told AFP.

He said the SDF was combing the city for any remaining jihadists who had not surrendered or been killed.

"The military operations in Raqqa have finished, but there are clearing operations now underway to uncover any sleeper cells there might be and remove mines," he said.

The announcement came just days after the SDF launched the final phase of its operation to retake the city.

There had been fears that the force, backed by the US-led coalition battling Islamic State in Syria and Iraq, could get bogged down in a protracted battle for the last 10 per cent of the city. But on Tuesday they captured the hospital and stadium in quick succession, effectively ending Islamic State's more than three-year presence in the city.

Sello said an official statement announcing "the liberation of the city" would be made soon.

The US-led coalition backing the operation made no statement on the city's capture, but announced that Islamic State had lost 87 per cent of the territory it seized in 2014 and hundreds of its fighters had surrendered.

"In the last few days, about 350 fighters surrendered to the SDF in Raqqa, with several confirmed foreign fighters taken into custody after SDF screening," Baghdad-based coalition spokesman Colonel Ryan Dillon told reporters in a video call.

"ISIS is losing in every way," he added in a tweet. "We've devastated their networks and eliminated leaders at all levels."

The breakthrough in the Raqqa operation, which was launched on 6 June, came after a deal was struck allowing the evacuation in recent days of civilians who had been held as human shields.

The battle for the city was fierce, with the Syrian Observatory for Human Rights monitor saying Tuesday at least 3,250 people had been killed, including 1,130 civilians, with hundreds more still missing.

Raqqa's capture leaves Islamic State in control of little more than a "dwarf territory" in neighbouring Deir Ezzor province, say observers.

Islamic State also controls territory in neighbouring regions on the Iraqi side of the border, where the jihadists are facing another US-backed offensive by Iraqi pro-government forces.