Ten members of the Kurdish YPG militia were also killed in the fighting in Hasaka province, a strategically important region that borders Turkey and Iraq and where Islamic State has recently lost ground, said Nasir Haj Mahmoud, a Kurdish official, speaking by phone.
“Daesh is trying to open new front,” Mahmoud said, using an Arabic term for Islamic State. He said the death toll among Islamic State fighters was as high as 41, and the dead included foreign fighters.
The latest battle between the enemies began when Islamic State fighters launched an attack between the towns of Tel Tamr and Tel Hamis, which the Kurdish militia seized from Islamic State in February, Mahmoud said.
The Syrian Observatory for Human Rights, a UK-based organization that monitors the war using a network of sources on the ground, said two dozen Islamic State fighters had been killed in fierce battles in the area.
Islamic State is still holding some 200 Assyrian Christians abducted from villages near Tel Tamr in February. There has been no word on their fate.
In recent weeks, Islamic State has mounted frequent attacks in areas far from its eastern strongholds in government- and rebel-held areas further west.
These have included an attempt to seize a Palestinian refugee camp on the Damascus outskirts, attacks on rival insurgents in Aleppo province, and a massacre in a village in a government-held part of Hama province.
The assaults are all well beyond the areas targeted to date in the U.S.-led aerial campaign focused mostly in the east and north.
Fighters believed to be members of Islamic State staged an attack on Friday in an area near a military airport in the southern province of Suweida, the Observatory reported.
It said at least 20 soldiers and pro-government militiamen were killed in the fighting, in addition to 15 insurgents.
The state news agency said the army had thwarted an attempt by Islamic State militants to infiltrate two villages in the area. It published a photo appearing to show the bodies of at least nine militants killed in the fighting.