Reports say hundreds of people, including pro-government fighters and their families, have been abducted or killed.
Syrian government forces have regained control over a hospital in the city of Deir Az-Zor, government sources told Al Jazeera, after ISIL seized it, killing 20 troops and taking medical staff hostage.
Steffanie Dekker, reporting from bordering Turkish city of Gaziantep, said that government forces also reportedly took back a university accommodation in the city.
Syria’s official news agency SANA reported that the military “eliminated a number of ISIS (ISIL) terrorists who had infiltrated a hospital in Deir Az-Zor city and taken doctors, patients, and other civilians hostage.”
“A source on the ground told SANA that army units clashed with a group of ISIS terrorists that had infiltrated al-Assad Hospital in Deir Az-Zor, which resulted in the death of the terrorists,” SANA reported.
ISIL, which controls most of Deir Az-Zor province, has stepped up its offensive to take more territory from the government there.
The hospital and the university dorm that the military said it had regained are located in the centre of an area that the government controls.
“The area has been surrounded and besieged by ISIL for months now … There has been fighting back and forth between both sides, but this was different because the attack came from multiple sides, from the north, west and the south,” Dekker said.
She also received reports that ISIL is trying to cut some vital supply lines for the Syrian government between a military airbase, a main brigade headquarters, and the centre of the city.
The Syrian Observatory for Human Rights, a UK-based monitoring group, said on Saturday that the fighters attacked Al-Assad hospital in Deir Az-Zor as they press an advance to control the oil-rich city and its vital airbase.
The attack sparked clashes with government forces providing security for the hospital in which six fighters were killed, the monitor said.
ISIL’s Amaq news agency said that the group also took control of a check point and a fire station in the city close to Syria’s eastern border with Iraq.
Amaq also said the fighters had taken territory near to the state-held military airport.
The fighters, who also control nearly all the surrounding province, have repeatedly attacked the government enclave and seized several neighbourhoods since the start of this year.