"Thousands of improvised explosive devices were planted in the district by Daesh," said Col. Mohammed Ibrahim said, using another name for ISIS. "Each one needs at least 30 minutes to be dismantled."
Soldiers are moving slowly through Ramadi's liberated neighborhoods looking for ISIS terrorists amid the IEDs. "We have to be very patient in order not to lose any soldier or any civilian in the area," Ibrahim said.
With the help of U.S.-led coalition airstrikes, Iraqi forces are continuing a coordinated attack on Ramadi, about 70 miles (113 kilometers) west of Baghdad and the capital of Anbar province.
The Iraqi flag has been hoisted over two recaptured Ramadi neighborhoods, the Joint Operations Command said.
ISIS took over Ramadi in May after a year of fighting there, spurring tens of thousands of civilians to flee.
Lt. Gen. Hamid Atiya al-Maliki, commander of Iraqi army aviation, said ISIS forces were collapsing and predicted that Ramadi could be liberated within days. He said ISIS fighters were planting explosives in civilian homes and using residences to carry out attacks.
Faisal al-Essawi, mayor of Amriyat al Falluja in Anbar, said about a third of Ramadi remained under ISIS control and that Iraqi troops had liberated four districts. There were an estimated 500 ISIS fighters, Essawi said.
On Friday, a security official in Ramadi denied ISIS claims that it shot down an Iraqi military helicopter near Humyra in southern Ramadi.
Tens of thousands of civilians remain in Ramadi, and "ISIS is surrounding them and preventing them from leaving," said Hikmet Suleiman, an adviser to the governor of Anbar province.
Iraqi forces had control of areas in Anbar before the latest push into Ramadi's center.
Two weeks ago, security forces started to encircle the city. On Tuesday, they were able to bridge a canal of the Euphrates River and close in on the city center, said Col. Steven Warren, a coalition spokesman.
The presence of Iraqi forces around Ramadi is "like a boa constrictor, a squeezing of ISIL out of that city," Warren said, referring to ISIS by another name.
He credits the yearlong U.S. training of Iraqi security forces for the successful advances. "That training is starting to take hold," he said.
Who is fighting?
Ramadi has strategic importance -- Anbar is the heartland of Iraq's Sunni Muslim population and the city is close to Baghdad.
Government officials said there are no Shiite militias involved in fighting on the front lines to liberate Ramadi.
Most of the ISIS militants still fighting there are foreign, Suhaib al-Rawi, the governor of Anbar province, told CNN on Thursday.
"The Iraqi security forces are advancing progressively. Daesh forces are totally fractured. Most of the Daesh fighters remaining in the city are foreign fighters," Rawi said.
Iraqi security forces, including the military, counterterror units and federal police, are conducting all the storming operations underway inside Ramadi's city limits, according to Suleiman, the adviser to Anbar's governor.
He said some Shiite militias are stationed on the southern outskirts of Ramadi but are not directly involved in ongoing operations, and Sunni militias made up primarily of Anbar tribesmen are tasked with holding ground recaptured by Iraq's military and clearing it of explosives.
Having Shiite militias battle in this Sunni stronghold was a concern of the central government, especially in securing support from local tribes in the fight against ISIS.
Why Ramadi matters
Ramadi also has symbolic significance. After Iraqi forces pulled out of the city
in the spring, U.S. Defense Secretary Ashton Carter questioned whether the Iraqis had the "will to fight."
Iraqi officials, including Prime Minister Haider al-Abadi, later said Carter had bad information. But Salim al-Jabouri, speaker of the Iraqi parliament and arguably the country's most powerful Sunni politician, said that even the Prime Minister
didn't know of the withdrawal until after it happened.
Ramadi was one of "three R's" identified as the core of a triple-pronged U.S. strategy against ISIS that Carter floated before U.S. lawmakers in October
. The others were raids by special operations forces and Raqqa, the extremists' de facto capital in Syria.