BEIRUT (Reuters) – Islamic State has asked the Syrian Army and its ally Hezbollah to let it withdraw from Syria’s border with Lebanon to the eastern province of Deir al-Zor, an official in the pro-Assad military alliance said on Thursday.

Syrian government forces and their Lebanese ally, Iranian-backed Hezbollah, are trying to oust Islamic State militants from the western Qalamoun region of Syria on Lebanon’s border.

The offensive began on Saturday, coinciding with a Lebanese army campaign on Lebanon’s side of the border to drive Islamic State from the Ras Baalbek area in the country’s northeast.

“Islamic State asked for negotiations and a withdrawal, and the Syrian side and Hezbollah agreed,” the official said.

Deir al-Zor province, which borders Iraq to the east, is almost entirely under Islamic State control. The Syrian government has held on to a pocket of territory in the provincial capital of Deir al-Zor city, and at nearby air base.

Both the pro-Assad military alliance and the Lebanese army have advanced towards the Syrian-Lebanese border from their respective sides. The Lebanese army has said it is not coordinating the assault with Hezbollah or the Syrian army.

Earlier this month, dozens of Nusra Front militants and thousands of Syrian refugees were transferred from Lebanon into rebel-held Syria in a deal negotiated between Hezbollah, the Syrian government and Nusra Front.

Hezbollah has provided critical military support to Syrian President Bashar al-Assad during Syria’s six-year-long war.

Its involvement in Syria is a cause of political tension in Beirut and has strained Lebanon’s policy of “dissociation” from regional conflicts.

Northeastern Lebanon was the scene of one of the worst spillovers of Syria’s war into Lebanon in 2014, when Islamic State and Nusra Front militants attacked the town of Arsal.