Members of the Iraqi Shiite militia Imam Ali Brigades, which belongs to the Shiite Popular Mobilization Forces, rest during a live-ammunition exercise in Najaf, southern Iraq, on Aug. 14. Iraqi Prime Minister Haider al-Abadi said that Shiite Popular Mobilization Forces will take part in the battle to reclaim Tal Afar despite calls to prevent Shiite militias from participating. (Khider Abbas/EPA)

Iraqi ground forces began an assault early Sunday on the town of Tal Afar, Prime Minister Haider al-Abadi announced on state television, one of the last territories in the country controlled by Islamic State militants.

The bid to reclaim Tal Afar comes one month after Iraqi forces, supported by U.S.-led airstrikes, declared victory in Mosul after a grueling nine-month battle that took a heavy toll on Iraqi troops and the hundreds of thousands of civilians that remained in the city during the fight.

Tal Afar, though much smaller than Mosul, is also expected to be a tough battle: Iraqi officials estimate that some 1,000 Islamic State militants remain in the town and will fight to the death, with little opportunity for escape. Tal Afar, about 43 miles west of Mosul, was surrounded in late 2016 in an effort by Iraqi forces to cut off Islamic State supply routes between the Syrian border and Mosul, the group’s de-facto capital in Iraq.

“I say to Daesh, you have no choice but to surrender or die,” Adabi said in a pre-dawn televised address, wearing his preferred black military fatigues and using the Arabic acronym for the Islamic State.

It will be the first test of Iraq’s military, particularly the elite U.S.-trained Counterterrorism Service, after it took significant losses during the battle for Mosul. The tempo of the battle will probably determine when Iraq will launch other campaigns to expel Islamic State fighters from at least two other sizable towns it still controls.

The town, about 37 miles east of the Syrian border, has both strategic and administrative significance to the Islamic State. It was one of the first waystations in Iraq for foreign fighters pouring into the country from Syria, and later became an important hub for supplies moving between the militants’ two largest holdings, Raqqa in Syria and Mosul.

It was also the home town of a number of the Iraqi Islamic State’s senior figures. Shortly after the U.S. invasion of Iraq in 2003, Tal Afar was one of the first places in the country to suffer a deadly wave of sectarian killings, and hosted an active al-Qaeda insurgency.

Before Islamic State militants claimed it in June 2014, Tal Afar was an ethnically diverse town where Shiites and Sunnis lived. The Islamic State either drove out or massacred the town’s Shiite population, drawing vows of revenge from the mostly Shiite militias that had been tasked with surrounding Tal Afar in November while the battle for Mosul kicked off.

The battle for Tal Afar will be closely watched by regional powers, given its strategic location near the border with both Syria and Turkey. Before Sunday’s bid to reclaim the town, there had been questions about which Iraqi forces would lead the assault. Turkey, along with the United States, had been eager for Abadi to sideline the powerful Iran-backed Shiite militias that surrounded the town, while Iran had been pushing for a major role for the militias.

Adabi was vague on the role the militias, which fall under nominal state authority, saying Sunday that Iraq’s military, counterterrorism forces and federal police would lead the fight, backed by the militias.

Salim reported from Baghdad.