The jihadists launched an offensive last Wednesday against areas held by the Syrian Democratic Forces coalition near to Ain Issa, a town held by the SDF some 50 kilometres (30 miles) from Raqa, killing 21 Kurdish fighters.
Late yesterday, "16 jihadists were killed and 19 wounded" in clashes with the SDF near Ain Issa, said Rami Abdel Rahman of the Syrian Observatory for Human Rights.
The SDF also recaptured an area seized by IS a few days earlier, he said.
On December 26, it seized the Tishreen Dam from IS along with several villages on the Euphrates' eastern bank.
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The dam, held by IS since 2014, helps generate electricity for large parts of the northern Aleppo province, the Observatory said.
It was the alliance's second major operation, after clearing IS from some 200 villages in the northeastern province of Hasakeh.
On the Euphrates' western bank, IS still controls swathes of territory stretching from Raqa to Jarablus, on the border with Turkey.
The conflict started as anti-government protests, but spiralled into a complicated multi-sided conflict.