The operation to retake Tikrit, which involves thousands of Iraqi soldiers, police and forces known as Popular Mobilisation units, which are dominated by Shiite militias, began on March 2.
It has succeeded in retaking towns leading to Tikrit, and also in surrounding several hundred jihadists in the city.
But capturing Tikrit itself has proved more difficult because of the jihadists' extensive defensive works, including a huge number of bombs planted in streets and buildings.
Iraq's interior minister announced last week that the operation had been halted temporarily to avoid casualties and to protect infrastructure in the city.
Army Staff Lieutenant General Abdulwahab al-Saadi, a top commander in Salaheddin province, told AFP on March 15 that coalition air support was needed in Tikrit, and that he had requested that the Iraqi defence minister ask for it.