Arab-Kurdish alliance 'seizes Raqqa Old City from IS'

US-backed fighters recaptured Raqqa's Old City on Friday, after weeks of battling Islamic State group militants, a spokesman confirmed, bringing them closer than ever to the jihadists' most well-defended positions.

"Our forces today seized full control of the Old City in Raqqa after clashes with Daesh," Syrian Democratic Forces spokesman Talal Sello said, using the Arabic acronym for IS.

"We are on the edges of IS' security quarter in the city centre, where most of its main bases are."

Sello declined to say when the alliance expected to seize all of Raqqa, but said operations were proceeding "according to schedule".

"Control over the Old City - which has historical importance - is a moral victory against IS, which is collapsing in Raqqa. Its defeat there is inevitable," he added.

IS overran Raqqa in 2014, transforming it into the de-facto Syrian capital of its self-declared "caliphate", which it declared three years ago on June 29.

The city became infamous as the scene of some of the group's worst atrocities, including public beheadings, and is thought to have been a hub for planning attacks overseas.

In August, reports said around 2,000 Islamic State fighters remain in Syria's Raqqa as US-backed Kurdish forces battle to recapture the city from the militant group.

The Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab fighters backed by US-led coalition warplanes, entered the city in June.

But the fighting has proved increasingly bloody for civilians still trapped in Raqqa, with one monitor reporting more than 160 civilians have been killed in coalition strikes in and around the city since August 14.

The United Nations estimates there are up to 25,000 civilians trapped inside the city, with food and fuel supplies short and prohibitively expensive.

The UN's humanitarian pointman for Syria, Jan Egeland, has said IS-held territory in Raqqa city is now "the worst place" in the war-torn country.

The Syrian conflict began when the Baath regime, in power since 1963 and led by President Bashar al-Assad, responded with military force to peaceful protests demanding democratic reforms during the Arab Spring wave of uprisings, triggering an armed rebellion fuelled by mass defections from the Syrian army.

According to independent monitors, hundreds of thousands of civilians have been killed in the war, mostly by the regime and its powerful allies, and millions have been displaced both inside and outside of Syria.