BEIRUT (Reuters) - The Syrian army and its allies have secured the Palmyra to Deir al-Zor road, a major supply route from government territory to the eastern city, defeating a strong Islamic State attack, a military media unit run by Lebanon’s Hezbollah said on Friday.

Smoke rises as Syrian army soldiers stand near a checkpoint in Deir al-Zor, Syria September 21, 2017. REUTERS/Omar Sanadiki

Islamic State’s assault, which began on Thursday, is the first major counterattack against the Syrian army and its allies since they broke through a swathe of territory to reach the city of Deir al-Zor this month.

“The Syrian army and its allies completely secured the Deir al-Zor-Palmyra highway after foiling the intense attack,” the Hezbollah media unit said. “The highway has become passable for traffic in both directions to and from Deir al-Zor.”

Hezbollah is one of the main allies of Syrian President Bashar al-Assad, alongside Russia, Iran and other Shi’ite militias.

Earlier on Friday, a commander in the military alliance backing Assad had said the road linking Deir al-Zor to Palmyra was being used only when absolutely necessary, and that the army and its allies were fighting to recover lost ground.

Islamic State had captured the town of al-Shoula, which sits on the highway, and the commander said at least 10 Hezbollah fighters had been killed in the fighting.

Islamic State said it had killed about 40 Syrian soldiers and captured several positions.

The Syrian army’s advance to Deir al-Zor, helped by the Russian military and Iranian-backed militias, lifted a three-year-long Islamic State siege 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.

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.

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