Iraqi security forces have launched an offensive to take back the city of Tal Afar, their next objective in the US-backed campaign to defeat Islamic State militants, Prime Minister Haider al-Abadi says.
"You either surrender, or die," Mr Abadi said in a televised speech announcing the offensive, addressing the militants.
A longtime stronghold of hardline Sunni Muslim insurgents, Tal Afar, 80km west of Mosul, experienced cycles of sectarian violence between Sunnis and Shi'ites after the US-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 Mr 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 US 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 US-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 US-trained Counter-Terrorism Service (CTS), who began encircling the city on Sunday.
The Shi'ite Popular Mobilisation 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.