The city is surrounded by Iraqi government troops and Shiite volunteers in the south, and Kurdish Peshmerga fighters in the north.
The coalition’s targets on Friday included weapons depots and command centers, in preparation for the ground assault.
About 2,000 battle-hardened militants remain in the city, according to the 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.
Waves of civilians have fled the city and surrounding villages under cover of darkness for weeks now, although several thousand are estimated to remain, threatened with death by the militants who have held a tight grip there since 2014.
Thousands of troops stand ready at the front-line, awaiting orders from Prime Minister Haider Al-Abadi to start the offensive, Iraqi army Maj. Gen. Uthman Al-Ghanimi said this week.
The main forces deployed around Tal Afar are the Iraqi army, federal police and the elite US-trained Counter-Terrorism Service (CTS), Iraqi commanders told Reuters.
Units from the Shiite Popular Mobilization Forces (PMF), some of which are trained and armed by Iran, are also likely to take part in the battle, as well as volunteers from Tal Afar fighting alongside government troops, they said.
Iraqi forces have already begun conducting air strikes aimed at “wearing them down and keeping them busy,” Iraqi military spokesman Brig. Gen. Yahya Rasool said.
Maj. Gen. Najm Al-Jabouri told Reuters last month he expected an easy fight in Tal Afar. He estimated fewer than 2,000 militants and their families were left there and they were “demoralized and worn down.”
“I don’t expect it will be a fierce battle even though the enemy is surrounded,” Al-Jabouri said.
Residents who left Tal Afar last week told Reuters the militants looked exhausted.
But Col. Ryan Dillon, a spokesman for the US-led coalition, said he “fully expects this to be a difficult fight.”
Lt. Col. Salah Abdul Abbas of the 16th Infantry Division, said they were bracing for guerrilla street-fighting fight, based on the lessons learned in West Mosul.
The UN’s International Organization for Migration (IOM), estimates that about 10,000 to 40,000 people are left in Tal Afar and surrounding villages. According to Iraqi commanders, the number of people left inside the city itself, including militants and their families, is closer to 5,000. However, aid groups say they are not expecting a huge civilian exodus as most of the city’s former residents have already left.
Meanwhile, gunmen killed seven family members of an Iraqi police officer in a pre-dawn attack Friday on their home near the northern city of Kirkuk, security officials told AFP.
A Kirkuk police captain, asking not to be named, said the unidentified assailants had kidnapped the seven family members, among them three of the officer’s children. The officer himself managed to escape during clashes between police and the gunmen, but the seven relatives including a son aged 15 were killed, he said.