What's Going On in Iraqi Offensive to Retake Fallujah From ISIS

— -- The Iraqi ground offensive to retake ISIS-held Fallujah began early Monday with Iraqi military forces pressing outside the city, in Anbar Province about 40 miles west of Baghdad.

Retaking the city has been a priority for the Iraqi government since early 2014, when it was one of the first parts of the country seized by ISIS. According to U.S. military officials, the number of ISIS fighters in the province has fallen to 1,000 as the group has sustained battlefield defeats in recent months.

The Fallujah military operation was announced late Sunday night by Iraqi Prime Minister Haider al-Abadi, who said Iraqi forces are "approaching a moment of great victory" against ISIS in the wake of recent gains in the far western town of Rutbah and other towns in the Euphrates River Valley.

WHAT IS THE IRAQI MILITARY DOING IN FALLUJAH?

Pentagon spokesman Capt. Jeff Davis said Monday that the Iraqi military had begun to conduct "shaping operations" outside Fallujah and had not entered the city. "Fallujah is important," he said. "It's the last remaining stronghold within Anbar province. It's the ISIS position closest to Baghdad and a place we're going to be working very closely with Iraqi partners to retake.”

The Fallujah operation involves forces from the Iraqi Counter Terrorism Service, the Iraqi army and Iraqi police. "Those forces have already begun to move on the city, where they're encountering some resistance,” said Davis. The shaping also involves striking targets in the city and "dropping leaflets meant to inform civilian populations to avoid ISIS areas ... They've been asking people to place white sheets on their roof to mark their locations."

While the U.S. is supporting the Iraqi military offensive in Fallujah, it is still not cooperating with the Iranian-backed Shiite militias known as the Popular Mobilization Forces, arrayed north of the city.

Davis said that he did not know what the role of the militias would be in Fallujah but that "they have largely a relationship of co-existence with Iraqi forces and are aligned against ISIS."

The U.S.-led coalition against ISIS has supported the ground operation with airstrikes — 21 in Fallujah since May 17, according to Davis. Iraq has not requested the use of American Apache helicopters based in Iraq as part of the Fallujah operation, though they remain available if needed.

WHY AN OFFENSIVE NOW?

In early 2014, ISIS found support among Iraq's dominant Sunni Muslim population, which resented the policies of the Shiite-led government of then–Prime Minister Nouri al-Maliki. Since then, retaking Fallujah has been a priority for the Iraqi government, even though it may not be as tactically important as it once was.

The U.S. military believes that about 1,000 ISIS fighters remain in Anbar province and that their numbers are decreasing. Davis said many ISIS fighters have left Anbar and particularly Fallujah, which he described as "a distant outpost for them" that has been "hard to sustain over time."

Two Iraqi army brigades have encircled the city for months in anticipation of a planned offensive, which seemed to await the slow progress of the Iraqi military in retaking Ramadi to the southwest.