The Syrian Democratic Forces (SDF) fought pitched battles on Sunday (August 13th) with the "Islamic State of Iraq and Syria" (ISIS) inside al-Raqa, AFP reported.

The two sides battled inside al-Raqa’s Old City, trading volleys of mortar rounds and heavy machine gun fire, said an AFP correspondent who was on the outskirts of the historic centre.

A coalition warplane provided air cover and bombed ISIS positions in the Old City.

"There is heavy fighting. Our forces are trying to surround more and more ISIS," said Nuri Mahmud, a spokesman for the Kurdish People’s Protection Units (YPG) which is fighting under the auspices of the SDF.

He said ISIS fighters were "using every means at their disposal to survive".

ISIS fighters have heavily mined the city to slow the SDF advance, and are also using booby-trapped cars, drones and suicide bombers.

Nevertheless the SDF has seized nine districts in the city's west and east since first entering al-Raqa on June 6th after a months-long campaign.

Meanwhile, the International Committee of the Red Cross (ICRC) warned on Monday that civilians fleeing the two remaining Syrian strongholds of ISIS -- al-Raqa and Deir Ezzor -- face "terrible, terrible conditions" in dozens of poorly-equipped informal camps.

Ingy Sedky, a Damascus-based spokeswoman for the ICRC, said more than 40 camps, each hosting anywhere between 2,000 and 10,000 people, had been set up in often-remote areas in al-Raqa and neighbouring al-Hasakeh.

"Fifty percent of the people inside these camps are children. They are living in terrible, terrible conditions because of the heat. It can be 50 degrees Celsius (122 Fahrenheit) during the day."

She said many camps lacked even the most basic items, including tents, with new arrivals sleeping in the open for up to 10 days while waiting for shelter.