US-backed Syrian forces advance against IS in southern Raqqa

The US-backed Syrian forces are on the verge of seizing full control of the southern neighbourhoods of IS-held Raqqa, an official said on Tuesday.

The US-led coalition said the Syrian Democratic Forces - an alliance of Kurdish and Arab fighters -  advancing from the east were within 300 metres of meeting up with those advancing from the west.

The SDF was making "consistent gains" every day, the coalition spokesman said.

On Monday, the World Health Organisation said there were critical shortages of medical supplies in Raqqa, where it estimated up to 50,000 civilians remained. Separately, Medecins Sans Frontieres said many sick and wounded people were trapped.

The SDF launched its US-backed campaign to seize Raqqa in early June. The assault on IS's de facto capital in Syria overlapped with the campaign to drive IS from the Iraqi city of Mosul, where the militant group was defeated last month.

The Kurdish official told Reuters SDF fighters advancing from the east and the west remain separated by a few streets where fighting continued.

Full control of the southern districts would sever IS's last remaining path to the Euphrates River which is to the south of the city.

"There is a fierce resistance from Daesh, so we can't determine when exactly we'll take (full control)," said the official, using an Arabic acronym for the extremist group.

"Around 90 per cent of the southern neighbourhoods are liberated," the official added.

The spokesman for the US-led coalition said SDF fighters had also captured around 10 square km of territory from IS north of Raqqa in the last two days.

"We've seen a less coherent IS defence in Raqqa compared to Mosul. IS is still using car bombs, booby traps, and civilians to hide behind, but their inability to address the multiple advances from the SDF is apparent," coalition spokesman Col. Ryan Dillon said.

Last week, the Syrian Observatory for Human Rights reported that the SDF has captured half of Raqqa.

The SDF is dominated by the Kurdish YPG militia, and is the main partner for the US-led coalition against IS in Syria.

IS has lost large expanses of territory in Syria over the last year to separate campaigns waged by the SDF, the Russian-backed Syrian military, and Turkey-backed Syrian rebels.