Islamic State group fighters unexpectedly took control of a town in Iraq’s western Anbar province Saturday. The surprise attack was the largest by the militant group in the desert region and left at least 19 policemen dead with others trapped inside their headquarters, officials told Reuters.

The Islamic State group, formerly known as ISIS, captured al-Wafa, 27 miles west of Anbar’s capital, Ramadi, after descending on the town Friday, Reuters reported. As the radical Muslim group presses toward the capital, ISIS currently controls three major towns west of Ramadi: Hit, Kubaisa and now al-Wafa.

Iraqi government forces have been immersed in a months-long battle for Ramadi and have struggled to arm Sunni tribes in western Iraq, where they are forming their own militias to fight ISIS. “Police forces have been fighting Islamic State fighters since Friday, but lack of ammunition forced it to retreat and losing the town. I’m frustrated because we were left alone without support,” al-Wafa Mayor Hussain Kassar told Reuters.

The Islamic State insurgency has seized swaths of western and northern areas in Iraq, with territory of the self-proclaimed caliphate stretching into Syria -- a key destination for international jihad fighters. The Sunni militant group captured Iraq’s second-largest city, Mosul, in June. Control of Mosul allows ISIS fighters and resources to flow across the border with Syria.

There are several separate entities fighting against the Islamic State group in Iraq, including the Iraqi Kurds, government security forces and groups of Sunni tribesmen in the west. Although all three want to stop ISIS from taking more of the country, there is little or no cooperation between them.

“The only way they are going to survive this is by working together,” Judith Yaphe, a professor at George Washington University’s Elliot School and an expert on Iraq, told an International Business Times reporter this week.