Iraqi pro-government forces advance towards Fallujah on May 23.
Fallujah, a longtime bastion of Sunni Muslim jihadists about 30 miles from Baghdad, was the first city to fall to ISIS militants in January 2014.
Iraqi soldiers move towards Fallujah on May 23.
Pro-government forces have surrounded Fallujah since last year, but they focused most combat operations on ISIS-held territories further west and north.
Iraqi forces on the move during the operation on May 23.
A member of the Iraqi forces gestures as smoke billows in the background during the advance towards Fallujah on May 23.
This long-awaited military offensive was backed by U.S.-led coalition airstrikes and paramilitary troops.
Shi'ite fighters launch a rocket towards ISIS militants on the outskirts of Fallujah on May 23.
An Iraqi soldier watches as smoke billows in the background during the operation of retaking Fallujah on May 23.
Federal police battalion commander, 1st Lt. Ahmed Mahdi Salih, said ground fighting was taking place around the town of Garma, east of Fallujah, which is considered the main supply line for the militants.
A member of the Iraqi forces mounts a gun atop a vehicle as they gather on the outskirts of Fallujah on May 22.
Iraqi forces get ready for the operation of retaking Fallujah, on May 23.