Iraqi security forces launched an offensive to take back the city of Tal Afar on Sunday, their next objective in the U.S.-backed campaign to defeat Islamic State militants, Prime Minister Haider al-Abadi said.
"You either surrender, or die," Abadi said in a televised speech announcing the offensive, addressing the militants.
A longtime stronghold of hardline Sunni Muslim insurgents, Tal Afar, 50 miles (80 km) west of Mosul, experienced cycles of sectarian violence between Sunnis and Shi'ites after the U.S.-led invasion of Iraq in 2003, and has produced some of Islamic State's most senior commanders.
The city was cut off from the rest of Islamic State-held territory in June. It is surrounded by Iraqi government troops and Shi'ite volunteers in the south, and Kurdish Peshmerga fighters in the north.
Hours before Abadi's announcement, the Iraqi air force dropped leaflets over the city telling the population to take precautions. "Prepare yourself, the battle is imminent and the victory is coming, God willing," the leaflets read.
About 2,000 battle-hardened militants remain in the city, according to U.S. and Iraqi military commanders.
They are expected to put up a tough fight, even though intelligence from inside the city indicates they have been exhausted by months of combat, aerial bombardments, and by the lack of fresh supplies.
"Intelligence gathered shows clearly that the remaining fighters are mainly foreign and Arab nationals with their families and that means they will fight until the last breath," Colonel Kareem al-Lami, from the Iraqi army's 9th Division, told Reuters.
Islamic State's self-proclaimed "caliphate" in effect collapsed last month, when U.S.-backed Iraqi forces completed the takeover of the militants' capital in Iraq, Mosul, after a nine-month campaign.
But parts of Iraq and Syria remain under Islamic State control, including Tal Afar, a city with a pre-war population of about 200,000.
The main forces taking part in the offensive are the Iraqi army, air force, Federal Police, and the elite U.S.-trained Counter-Terrorism Service (CTS), who began encircling the city on Sunday.
The Shi'ite Popular Mobilization Forces (PMF), some of whom are trained and armed by Iran, confirmed they are also taking part in the battle. Their involvement is likely to worry Turkey, which claims an affinity with the area's predominantly ethnic Turkmen population.
The U.S.-led coalition said that in recent days it has carried out dozens of air strikes on Tal Afar, targeting weapons depots and command centers.
Lieutenant General Jeffrey Harrigian, the top U.S. Air Force commander in the Middle East, told Reuters he expected U.S. air support to remain steady as the Iraqis initiate their advance, after two weeks or so that have averaged about 10-15 strikes around the city.
"I would expect something similar to that because they're still on the outskirts [of Tal Afar], beginning the initial parts of the operation," said Harrigian.
U.S. commanders say Tal Afar's complicated geography, with ridge lines around city that could provide shooting positions for Islamic State fighters, will heighten the need for overhead imagery, and the ability strike.
"We clearly need to be in position to ensure that we are providing the eyes on the other side of the hill for the Iraqis," Harrigian said.
Islamic State claimed to have successfully targeted several vehicles belonging to Shi'ite militia groups to the east and west of Tal Afar, in a statement published on the group's Amaq news agency on Sunday.
Lami said Tal Afar's wide streets would allow tanks and armored vehicles easy passage. Only one part of Tal Afar, Sarai, is comparable to Mosul's Old City, where Iraqi troops were forced to advance on foot through narrow streets in a battle that resulted in the near total destruction of the historic district.
Preserving the lives of civilians during the campaign remains a priority, Iraqi military spokesman Brigadier General Yahya Rasool told al-Iraqiya TV on Sunday.
Waves of civilians have fled the city and surrounding villages under cover of darkness over the past weeks, although several thousand are estimated to remain, threatened with death by the militants who have held a tight grip there since 2014.
Residents who left Tal Afar last week told Reuters the militants looked exhausted.
"[Fighters] have been using tunnels to move from place to place to avoid air strikes," said 60-year-old Haj Mahmoud, a retired teacher. "Their faces looked desperate and broken."
The United Nations International Organization for Migration (IOM), estimates that between 10,000 to 40,000 people are left in Tal Afar and surrounding villages.