BEIRUT (Reuters) – The Syrian army and its allies fought on Friday to recover ground lost during an Islamic State counterattack in eastern Syria that targeted positions on the road to Deir al-Zor, a commander in the pro-Damascus alliance said.

The assault that began on Thursday marks the first major counterattack against the Syrian army and its allies since they broke through a swathe of Islamic State-held territory to reach the city of Deir al-Zor earlier this month.

“They took a number of positions. We absorbed the attack and work is under way to recover the positions,” the commander, speaking on condition of anonymity, told Reuters. Areas lost to Islamic State included the town of al-Shoula, which sits on the road connecting Deir al-Zor to western Syria.

The commander said the road linking Deir al-Zor city to the city of Palmyra was only being used in cases of absolute necessity. A media unit run by Lebanon’s Hezbollah, which is fighting in support of Damascus, said the road was secure.

Helped by the Russian military and Iran-backed militias, the Syrian army’s advance to Deir al-Zor lifted a three-year-long siege imposed by Islamic State on a government-held enclave in the city.

The Syrian Observatory for Human Rights said the Islamic State attacks had killed more than 58 fighters from the Syrian army and allied forces since Thursday.

Islamic State said on Thursday it had killed around 100 government fighters south of the town of al-Sukhna, which is also located on the road to Deir al-Zor, and announced it had taken a hill overlooking the town.

A U.S.-backed alliance of Syrian militias, the Syrian Democratic Forces, is waging a separate offensive against Islamic State in Deir al-Zor to the east of the Euphrates River, which bisects the province.

Islamic State leader Abu Bakr al-Baghdadi pressed his followers to “stand fast” and keep fighting in an undated recorded statement released on Thursday.

(Reporting by Sarah Dadouch and Laila Bassam; Editing by Tom Perry and Toby Chopra)