ISIS militants launched their biggest attack in months on regime-held areas in the contested city of Deir al-Zor on Saturday, leaving dozens of dead, a war monitor said.
The militant group attacked the city from several sides, the Syrian government and opposition activists said.
At least six large explosions rocked the city since dawn as the militants clashed with the army and allied forces, the British-based Syrian Observatory for Human Rights reported.
Intense fighting broke out between regime troops and ISIS militants in the city and in the vicinity of a nearby military airport controlled by regime forces after the militants launched their multi-pronged attack starting from the area of Baghaliyeh near the northwestern tip of the city.
Syrian regime warplanes hit back against ISIS positions, the Observatory and state media said.
Syrian state news agency SANA said the army was repelling attacks by the ultra-hardline jihadist group along several frontlines, including around the military airport controlled by the regime.
ISIS shelling killed three people and wounded nine in residential regime-held districts, SANA reported.
The fighting and bombardment killed at least 12 government forces and 20 Islamic State fighters, the Observatory said.
Islamic State controls most of Deir al-Zor province, which borders Iraq, including more than half the city, and has besieged the remaining government-held areas of the city for nearly two years.
The Syrian regime and its Russian ally have made regular aid drops into the encircled zone, where about 200,000 people live, lacking food and medicine.
Deir al-Zor province links ISIS’ de facto capital in the Syrian city of Raqqa with territory controlled by the militant group in Iraq.