Iraqi troops are more than halfway through an operation to encircle Daesh militants in Ramadi, after which they will launch a final offensive to retake the Iraqi city, said US Air Force Colonel Pat Ryder, the spokesman for the US Central Command.

The Iraqi forces are progressing in the fourth week of their effort to isolate and cut off Daesh fighters, who have been controlling Ramadi for three months now.

"The objective here is to cut off [Daesh]'s lines of communications to prevent or limit their resupply and reinforcement," Ryder, said in a telephone briefing with Pentagon reporters.

He said Iraqi troops are engaged in "tough, dangerous work" to encircle the city and then prevent Daesh from bringing in more troops or supplies.

The militants are trying to slow or stop Iraqi forces by using hidden explosive devices, improvised explosives in vehicles, suicide bombers and fighters, Ryder said.

The Iraqis have used armored bulldozers and other specialized equipment to remove explosives.

"The Iraqis are continuing to move forward, executing this complex operation as they had planned it," Ryder said. "They have ... a good plan. They're executing that plan at the timeline they have set for themselves.