BAGHDAD/ERBIL, Iraq - Iraqi security forces launched an offensive to take back the city of Tal Afar on Sunday, their next objective in the US-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 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 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.