Kurdish-led fighters marching against IS near Syria's Raqqa

The Syrian Kurdish-led force fighting the Islamic State group north of the country is on the verge of surrounding a wide area north of the IS stronghold of Raqqa, a spokeswoman for the group said on Thursday.

US-backed Syria Democratic Forces [SDF] fighters are advancing on two fronts north of Raqqa, the de facto capital of IS' self-declared caliphate, Cihan Ehmed told AP.

"The operations are ongoing according to the plan," she said.

The push from Ein Issa and Suluk north of Raqqa has been ongoing for days under the cover of airstrikes by the US-led coalition.

Ehmed said once the forces coming from the two directions meet north of Raqqa, they will surround 550 square kilometres (212 square miles) of territory controlled by the extremists.

Scores of people are fleeing areas of fighting north of Raqqa, the London-based Syrian Observatory for Human Rights said, also noting the SDF advance north of Raqqa.

Later on Thursday, the SDF said on social media that its fighters have captured three farms, a village, and have approached the village of Hayes where intense clashes are ongoing.

The operation to seize Raqqa has been dubbed "Euphrates Rage" and a joint operations command has been set up to coordinate various factions taking part in the battles.

The SDF, which includes Kurdish, Arab, Syriac and Turkmen fighters, say they have committed 30,000 fighters to the offensive aiming to eventual recapture the city of Raqqa, which was announced on Sunday.

The US-led coalition is currently flying dozens of aerial missions over the Raqqa region in support of Washington-backed Kurdish fighters advancing on the city.

On Wednesday, Syrian activists accused the US-led coalition currently conducting airstrikes on Islamic State targets in Syria of killing civilians in attacks in Raqqa.

A spokesman for the US-led forces has since said that the coalition has conducted airstrikes in the area but did not confirm claims of civilian casualties. 

“More information is needed to conclusively determine responsibility,” said US Col. John Dorrian, in comments published in The Associated Press.