The Iraqi army suffered minimal casualties in the battle for Ramadi as most of the Islamic State fighters defending the city fled to surrounding areas or were killed in U.S. airstrikes, a U.S. defense official said.

"As far as the downtown Ramadi area, we have not seen significant combat power" from Islamic State forces, Army Col. Steve Warren, a Defense Department spokesman in Baghdad, said Tuesday.

"[Iraqi] casualty counts are generally low ... really in the low double digits, if that, you know, in the 10s or 20s," Warren said in a news briefing.

The Iraqis appear to have faced far less resistance than the U.S. troops who conducted a similar operation in Ramadi in 2006. More than 70 U.S. troops were killed in the five-month fight led by the U.S. Army and Marine Corps.

After more than seven months of preparation following the Islamic State group's seizure of Ramadi in May, Iraqi forces pushed into the city center last week, crossing a key canal with the help of a temporary bridge provided by the U.S. Army.

U.S. and Iraqi officials say the bulk of the combat effort came from airstrikes provided by the U.S. and its allies.

The Iraqis' assault on the city marks the first major battlefield victory for that nation's forces since they collapsed in the face of an Islamic State group advance across northern Iraq in June 2014.

Iraqi Prime Minister Haider al-Abadi said the retaking of Ramadi is the beginning of the end for the Islamic State group, also known as ISIS or ISIL.

"2016 will be the year of the big and final victory, when [the Islamic State's] presence in Iraq will be terminated," Abadi said in a televised speech Monday. "We are coming to liberate Mosul, and it will be the fatal and final blow."

On Tuesday, after raising the Iraqi flag over downtown Ramadi's provincial government center, the Iraqi army was moving block by block through the city. The bulk of the ISIS fighters appeared to have retreated to territory east of the city along the Euphrates River that is still held by the extremists, Warren said.

The operation did not involve support from ground-level U.S. combat advisers or attack helicopters. Top U.S. officials offered to provide that support in early December, but the Iraqi government declined.

The size of the Islamic State force that seized Ramadi in May probably peaked at nearly 1,000 fighters. U.S. airstrikes helped diminish that to 250 to 350 during the past week as the Iraqi army began its invasion of the city center. Of those fighters, U.S. airstrikes likely killed about 100 during the past week, Warren said.

The Iraqi army's operation in Ramadi was led by Shiite-dominated units, which are expected to "clear" the city and then pull back to allow a Sunni tribal force to move in and "hold" the area. Ramadi is a Sunni city and a Sunni force in the city is considered essential for long-term security.

"Right now, we envision the Iraqi security forces moving to other battlefields," Warren said.

The U.S. has helped to train about 5,000 Sunni tribal fighters, he added.

A key remaining question is whether Islamic State militants who have left Ramadi will retreat into other parts of Iraq and Syria or whether some significant force will remain to conduct an insurgency-style campaign against the Iraqi forces that try to hold Ramadi.

"It's a little early to tell right now," Warren said. "It is certainly something that we're keeping an eye on.

"It stands to reason that they may attempt to adopt insurgency and guerrilla tactics. That's part of the reason why we want Sunni tribal fighters who are from this area. Your best defense against this type of thing is competent locals who understand their neighborhoods and their towns and are much, much more able to counter these type of insurgent or guerrilla campaigns."

Andrew Tilghman is the executive editor for Military Times. He is a former Military Times Pentagon reporter and served as a Middle East correspondent for the Stars and Stripes. Before covering the military, he worked as a reporter for the Houston Chronicle in Texas, the Albany Times Union in New York and The Associated Press in Milwaukee.

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