After months of retreat in northern Syria, the Islamic State has hit back at pro-Assad forces in Raqqa Province, killing scores of troops.

Local reports indicated ISIS seized vehicles and pushed back the offensive near the town of Maadan, with at least 34 regime and allied troops slain. Some accounts said the toll was far higher.

Syrian State media and pro-regime outlets were silent about the setback, continuing to post story after story proclaiming victories. However, one pro-Assad account summarized — purportedly from military sources — that while the paramilitary Tiger Forces shored up some points, local allies “continued falling one after the other”. By early Saturday, about 23 km (14 miles) had been lost along the Euphrates River.

A fighter in the Tiger Forces denounced the local allied units as “the utmost of randomness, chaotic [sic], and recklessness”.

ISIS media channels posted images of an attacked Syrian army convoy and the bodies of more than a dozen soldiers.

Pro-Assad forces had hoped to complete the defeat of ISIS in southern Raqqa Province and then drive into Deir ez-Zor Province, the last major position of the Islamic State, in eastern Syria. The Assad regime is hoping to reopen links with the Iraqi border and to retake the divided city of Deir ez-Zor, surrounded by ISIS since 2014.

But the ISIS counter-attack has pushed pro-Assad forces about 30 km (19 miles) west of Maadan while regaining territory along the Euphrates where Tiger Forces had “fought the fiercest battles” to claim the area, according to the pro-Assad account.

Maadan is about halfway between Deir ez-Zor city and Raqqa city, where the US-backed, Kurdish-led Syrian Democratic Forces have been trying for months to recapture the central ISIS position in northern Syria.