Shiite fighters and Sunni fighters, who have joined Shiite militia groups known collectively as Hashid Shaabi ("Popular Mobilization") to fight the Islamic State, gesture Tuesday next to former Iraqi President Saddam Hussein's palaces in the Iraqi town of Ouja, near Tikrit. Thaier Al-Sudani/Reuters/Landov hide caption

itoggle caption Thaier Al-Sudani/Reuters/Landov

Shiite militiamen pose with their banner (right) next to a captured — and upside-down — ISIS flag (left) in Tikrit, Iraq. Militias are bolstering Iraqi forces in a major operation to retake the city from the self-proclaimed Islamic State. Mohammed al-Mozani/AP hide caption

itoggle caption Mohammed al-Mozani/AP

Iraq's push into Tikrit follows its retaking of the nearby town of al-Alam on Tuesday. There, a woman welcomed a relative who is fighting with a militia that's backing Iraqi troops. Thaier al-Sudani/Reuters /Landov hide caption

itoggle caption Thaier al-Sudani/Reuters /Landov

ISIS militants at al-Sharqat base north of Tikrit, Iraq. The al-Qaida-linked group has captured Mosul as well as Tikrit. This image came from a video posted by IraqiRevolution, a group that supports ISIS. AP hide caption

itoggle caption AP