Parts of the Iraqi city of Beiji have been taken back by Iraqi security forces and Iranian-backed Shiite fighters, a U.S. defense official confirmed to Fox News Monday.

The unnamed official-- who had been briefed on the latest intelligence from Iraq-- told Fox that Islamic State fighters still occupy some areas in the city, a strategic focus because of its proximity to an oil refinery.

“They still have a foothold in both,” the official said, referring to both parts of the town and the refinery. 

The official said that Iraqi security forces attacked from the south into Beiji and pushed “some elements” of ISIS fighters away from “a few” government buildings over the weekend. 

News of the gains comes after the crushing fall of Ramadi-- the capital of Anbar province-- to ISIS fighters last month.

The U.S.-led coalition has carried out three airstrikes in the Beiji area since the weekend, according to U.S. Central Command. The most recent strike list released Sunday confirmed there were two airstrikes near Beiji over the weekend-- striking an ISIS tactical unit and a bridge, destroying “an ISIL vehicle.”

The commander of Iraq’s Interior Ministry Quick Reaction Forces, Brig. Gen. Nassir al-Fartousi, told state TV Sunday that the Iraqi flag was raised over a local government building in Beiji and that troops were advancing to other areas.

The spokesman of Joint Operations Command, Brig. Gen. Saad Maan Ibrahim, said the security forces "are now controlling" the downtown Beiji area, describing the advance as an "important victory."

"The enemy has suffered a defeat and has sustained heavy losses and we hope that the whole city will be cleared within few days," Maan told The Associated Press in a brief interview, saying "dozens" of ISIS militants had been killed.

Maan said the capture of Beiji would help Iraqi forces to better secure the nearby Beiji refinery -- Iraq's largest oil refining facility and key to the country's domestic supplies.

Beiji, some 155 miles north of Baghdad, fell to the extremist ISIS group during its blitz across northern Iraq nearly a year ago, but the refinery facility has remained contested ground with ISIS militants and government forces battling for control. The town is also strategically significant as it lies on the road to IS-held Mosul, Iraq's second largest city.

Iraqi and Kurdish forces have managed to roll back the ISIS group in many parts of the country with the help of U.S.-led airstrikes, and recaptured the northern city of Tikrit in April.

The ISIS group has declared an Islamic caliphate in the territories it controls in Syria and Iraq, and has used oil smuggling to finance much of its operations.

Fox’s Jennifer Griffin and Lucas Tomlinson, and the Associated Press contributed to this report.