The Iraqi government said the long-awaited battle to recapture the city of Fallujah began in the early hours of Monday. Video published online overnight purportedly shows heavy bombardment of the city before the advance of ground troops.
Prime Minister Haider al Abadi made a televised announcement that the operation had begun, vowing that Iraqi forces would "tear up the black flags" of the Islamic State of Iraq and Syria (ISIS) in Fallujah.
Backed up by U.S. and coalition airstrikes, a combination of Iraqi troops, police and Shiite militias made early progress, pushing ISIS militants back out of the farmland surrounding the city and toward Fallujah itself.
There are an estimated 800-1,000 ISIS fighters in Fallujah, which has been extensively fortified with trenchs and minefields. Coming after them are upwards of 20,000 Iraqi forces, led by 1,500 members of the Counter Terrorism Services, 10,000 regular Army troops (many trained by the U.S.) and 8-10,000 Iraqi national police.
The U.S.-led coalition carried out at least seven strikes in and around Fallujah in the last week. And the Iraqi military said its own U.S.-supplied F-16 warplanes had bombed suspected ISIS hideouts in the city.
U.S. officials tell CBS News that American military advisers will not go forward into Fallujah with the Iraqi forces, but some U.S. artillery at the Taqaddum air base, west of Fallujah, can reach targets in the ISIS-held city and may be put to use.
American Apache helicopter gunships are also available, have not been requested as support by the Iraqis yet.
Thus far, U.S. and coalition airstrikes have been against fixed targets in the city, such as IED factories and command centers, but American commanders expect that once the fighting intensifies and ISIS starts maneuvering, the number of requested strikes will pick up.
The commander of the operation, Lt. General Abdul-Wahab al-Saadi, said Monday that ground fighting was taking place around the town of Garma, east of the city.
CBS News was with Iraqi forces near Garma just a couple of weeks ago, where they were holding a zigzag of a front line against the extremist fighters.
There weren't any trenches or bunkers. The soldiers took up fighting positions anywhere they could -- mostly in abandoned homes or buildings flattened by one of the dozens of airstrikes to hit the area over the last two years.
They didn't have much more than the weapons they were carrying and a few bullet-ridden Humvees left behind by American forces.
That front line had not moved an inch in more than a year. We were told they were trying to lure ISIS militants out into the fight, in order to give away their positions or draw them into the open, making them vulnerable to airstrikes.
The soldiers were jittery.
In the tall reeds that surround the city, they couldn't see the enemy coming, and said they were vulnerable to the typical ISIS plan of attack: a suicide car bomb or truck, followed by an ambush.
Saadi said he couldn't predict how long it would take to oust ISIS from the city -- which sits just 40 miles west of Baghdad and was overrun by the militants in January 2014. The city is expected to be heavily mined and ISIS may have entrenched snipers.
Fallujah became the epicenter of the insurgency against U.S. forces after the 2002 invasion that toppled Saddam Hussein. It was in Fallujah that al Qaeda in Iraq found its stronghold, and put up a fierce resistance that saw 100 American troops killed in 2004.
Al Qaeda in Iraq morphed in later years into ISIS.