Iraqi security forces and Shiite fighters fire artillery during clashes with ISIS militants in Salahuddin province. The push to retake Tikrit is being aided by Iran, which is providing rockets and other support to Iraq. THAIER AL-SUDANI/Reuters /Landov hide caption

itoggle caption THAIER AL-SUDANI/Reuters /Landov

Members of Iraqi security forces drive toward an area south of Tikrit, Iraq, over the weekend. An Iraqi force has launched a military offensive, hoping to push ISIS out of Tikrit. AHMAD AL-RUBAYE/AFP/Getty Images hide caption

itoggle caption AHMAD AL-RUBAYE/AFP/Getty Images

Then-U.S. ambassador to Iraq Christopher Hill (right) tours the Mosul Museum of History in May 2009. This week the self-declared Islamic State posted a video online that showed militants going through the museum, pushing over statues and smashing artifacts with sledgehammers. Mujahed Mohammed/AFP/Getty Images hide caption

itoggle caption Mujahed Mohammed/AFP/Getty Images

An Iraqi child who fled fighting between the so-called Islamic State and Kurdish peshmerga is among the some 3,000 people living at the Baharka camp, near Irbil, the capital of the Kurdish autonomous region in northern Iraq, on Jan. 16. Safin Hamed/AFP/Getty Images hide caption

itoggle caption Safin Hamed/AFP/Getty Images

Training at a new camp near the front line, a mix of Arabs and Kurds prepare for an assault on Mosul in upcoming months. The men will wear balaclavas to conceal their identities while they fight, because they have family in Mosul and don't want to put their relatives at risk. Ari Shapiro/NPR hide caption

itoggle caption Ari Shapiro/NPR

Iraq is preparing to take back Mosul, a senior U.S. military official says. Earlier this month, government-backed Sunni Arab tribesmen who've been training to fight ISIS marched northeast of Mosul, in northern Iraq. Yaser Jawad/Xinhua /Landov hide caption

itoggle caption Yaser Jawad/Xinhua /Landov