Cihan Ehmed of the US-backed Syria Democratic Forces told The Associated Press on Thursday that its fighters are advancing on two fronts north of Raqqa, the de facto capital of IS' self-declared caliphate.
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.
The US-backed 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.
Ehmed said once the forces coming from the two directions meet north of Raqqa, they will surround 550 square kilometers (212 square miles) of territory controlled by the extremists.
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"The operations are ongoing according to the plan," she said. The Britain-based Syrian Observatory for Human Rights said many people are fleeing areas of fighting north of Raqqa.
It added that SDF fighters have advanced north of Raqqa, capturing new areas and raising to 17 the number of villages and farms taken from IS since the offensive began.
The operation to recapture Raqqa has been dubbed "Euphrates Rage" and a joint operations command has been set up to coordinate various factions taking part in the battles.
Elsewhere in Syria, a rocket fired by rebels struck a school in the capital Damascus' central al-Mohajireen neighborhood wounding three children, state media said without providing further details.
In the rebel-held Damascus suburbs of Douma and Saqba, government airstrikes killed at least 11 civilians, including four children and three women, according to the Syrian Civil Defense in Damascus suburbs. The Observatory also said 11 were killed, but said they included four women.