Five Iraqi troops were killed on Thursday when their helicopter crashed on a "combat mission" north of Baghdad.
A security source confirmed to AFP that the helicopter had been hit by ground fire.
The helicopter came down near Amerli in Salaheddin province, the military said, in an area where Iraqi troops have carried out repeated operations against suspected ISIS sleeper cells.
Video footage of the helicopter crash sent to journalists in Baghdad showed firefighters attempting to put out a blaze in the wreckage of the aircraft.
The security forces had launched an operation on Tuesday to "search and clear areas in the south of Kirkuk province", which borders Salaheddin, a statement on their Twitter account said.
The security source told AFP that the helicopter that came down was one of two that had been checking pylons carrying high-voltage power lines in the area, a frequent target for holdout terrorists in recent months.
As the two aircraft approached Amerli district, one of them took a "direct hit" which forced it down.
ISIS lost its last territory in Iraq in 2017 after a bloody three-year campaign that put paid to its hopes of forging a transnational "caliphate" straddling the border with Syria.
But the insurgents retain sleeper cells in desert and mountain areas that they have used as launchpads for attacks in Iraq's cities.
A July 19 suicide bombing claimed by the Sunni extremists killed 30 people in a street market in a Shiite district of Baghdad.
Elsewhere in the country, at least two rockets hit Baghdad's Green Zone early on Thursday but caused no casualties, Iraqi security sources said.
One rocket landed in a parking lot inside the Green Zone and a second one hit a nearby empty area.
The dawn attack came as Prime Minister Mustafa Al Kadhimi was flying home from Washington after White House talks in which President Joe Biden announced an end to US combat operations in Iraq.