Islamic State (ISIS) group fighters attacked a town near their de facto Syrian capital Monday in a bid to recapture it from Kurdish and Arab rebel forces, a Kurdish spokesman told the AFP news agency.
"ISIS launched a large-scale offensive at dawn… and managed to enter Ain Issa," said Redur Khalil, a spokesman for the Kurdish People's Protection Units.
"Clashes are continuing inside the town in the southern part to expel ISIS," he told AFP.
Ain Issa is some 55 kilometers (35 miles) north of IS's de facto Syrian capital of Raqa city, and fell to Kurdish and Arab forces on June 23, shortly after they took the border town of Tal Abyad from the jihadists.
The Syrian Observatory for Human Rights, meanwhile, said that the ISIS attack had succeeded and jihadist fighters were in control of Ain Issa and several nearby villages after a wide-ranging assault.
The Britain-based monitor said ISIS had launched a counter-attack against fronts in both Raqa province and neighboring Hasakeh.
Kurdish and rebel spokesmen also said ISIS was engaged in a large-scale attack in the two provinces, but denied Ain Issa had fallen.
According to the Observatory, 37 ISIS fighters have been killed and 46 wounded along a front line stretching between the provinces since Monday's assault began.
The wounded ISIS members have been taken to hospital in Raqa.
"The jihadists were killed and wounded in fighting and shelling," Observatory director Rami Abdel Rahman told AFP.
There were also Kurdish casualties, but the numbers were not yet known.
Kurdish fighters backed by Arab allies seized the frontier town of Tal Abyad from ISIS on June 16, after weeks of fighting during which they captured numerous villages in Raqa province from the jihadists.
The fall of Tal Abyad was a major blow for the group, which had used the town as a conduit for weapons and fighters.
After its capture, the anti-ISIS forces advanced to Ain Issa, taking both it and a former military base nearby.
But in recent weeks, ISIS forces have launched several counterattacks against the Kurds, including in Kobane, a small border town the jihadists had battled to capture for some four months.
ISIS has seized large swathes of territory in Syria and Iraq since 2013 and declared an Islamic "caliphate" in the land under its control.
The jihadists have carried out numerous atrocities in areas they control, ranging from public beheadings to enslavement and mass rape.
AFP contributed to this report.