Shiite fighters gather during a military operation in the west of Samarra, in the desert of Anbar, March 7, 2016.

Tens of thousands of trapped civilians have stalled Iraqi forces fighting ISIS in the country’s western Anbar province, the spokesman for Iraq’s elite counterterrorism forces told the Associated Press Friday.

Iraqi forces re-launched an offensive on the town of Hit, 85 miles (140 kilometers) west of Baghdad, under cover of heavy coalition airstrikes early Thursday morning, Sabah al-Numan said. Over the past week the U.S.-led coalition launched 17 airstrikes in and around Hit, according to Pentagon statements.

Hit lies along an ISIS supply line linking the group’s extremist forces in Iraq to those in Syria. Iraqi commanders say retaking the town is key to building on their current momentum after retaking Ramadi earlier this year and linking up government forces to the west and the north of Baghdad in preparation for an eventual push on Mosul.

The counterterrorism forces, who are leading the Hit operation, reached within three kilometers of the city center Thursday before being forced to stop, al-Numan said. “The commanders are making a plan to evacuate these families,” Al-Numan said, adding that leaflets were dropped over Hit indicating which roads can be used to flee safely.

Iraqi forces encountered similar problems when trying to clear Ramadi, the provincial capital of Anbar, of ISIS fighters earlier this year. As government forces advanced across downtown Ramadi, the extremists pulled back and took civilian captives with them as shields.

The tactic significantly slowed the advance of ground troops. While downtown Ramadi was declared under government control in December 2015, it wasn’t until two months later that Iraqi and coalition forces said the rest of the city was “fully liberated.”

After storming across Iraq in the summer of 2014, over-running Iraq’s second largest city of Mosul, ISIS still controls large swaths of territory in the country’s north and west.

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