The operation by the US-led coalition had been requested by Prime Minister Haider al-Abadi, a Pentagon spokesman said Wednesday.
The strikes would target only Islamic State forces and would avoid civilian casualties or damage to infrastructure where possible, General James Terry told the German news agency dpa.
Iraqi and allied forces, comprised of more than 20,000 Shiite militia fighters, are in the middle of an offensive to retake the city.
The militias have vowed revenge for the apparent mass execution of up to 1,200 Shiite army recruits by Islamic State forces during the lightning offensive last June that saw the jihadists seize Tikrit, Iraq's second city of Mosul, and other mainly Sunni areas.
