Daesh militants on Monday captured the town of Ain Issa from the Kurdish fighters following a massive assault that left tens of Kurdish fighters killed, a monitor group reported.

The IS militants fully recaptured the town of Ain Issa and its surrounding areas in the eastern countryside of the northern province of Raqqa, the de facto capital of the IS terror group.

The IS lost the town to the Kurds last month, as part of a series of setbacks the IS suffered by the hands of the Kurdish fighters of the People Protection Units (YPG).

The Syrian Observatory for Human Rights said the terror-labeled group launched a counter-offensive to retake the town on Monday, targeting the positions of the YPG across a wide area in the town of Alieh in the outskirts of the northeastern province of Hasaka, all the way through northern Raqqa toward the Kurdish city of Ayn al-Arab, or Kobane, in the northwest of Syria.

Tens of the YPG fighters were killed in the IS assault, said the Observatory. Other activist group placed the number of dead Kurdish fighters at 50.

The importance of Ain Issa emanates from its proximity to the city of Raqaa, the stronghold of the IS. When the town was taken by the Kurds, the IS felt threatened as the YPG fighters were only 30 km from the Raqqa city.