Although they no longer hold territory, IS sleeper cells were believed to be hiding out in vast deserts and scraggy mountains like Hamreen, from where they have conducted deadly hit-and-run attacks against government posts.

Iraqi military spokesman General Yahya Rasool said Prime Minister Adel Abdel Mahdi had ordered the Counter-Terrorism Service "to conduct operations targeting Daesh (IS) remnants and their caves in the Hamreen Mountains."

The operation was supported by both Iraqi aircraft and US-led coalition warplanes, he said in an online statement.

CTS spokesman Sabah al-Naaman said the operation had lasted four days, with troops parachuting in and setting fire to 15 IS shelters.

Among them was a centre used to produce IS's weekly propaganda magazine Al-Naba.

"A special team is currently analysing the seized computers and documents -- and we'll see if there's a new issue, as they are usually published on Thursdays," Naaman said.

The force is planning similar operations in other parts of Iraq.

"The important part of this operation is that this difficult area, which posed a threat to northern Diyala and southern Kirkuk, has been cleared out," Naaman added.

IS swept across swathes of Iraq and Syria in 2014, declaring a self-styled "caliphate" that ruled with an iron fist.

But it lost its territorial hold on Iraq in late 2017, and US-backed forces wrested the last piece of land in neighbouring Syria from the jihadists last month.

Still, escapee jihadists have kept up guerilla attacks, especially in rural Sunni-majority areas in the provinces of Salaheddin, Kirkuk, Anbar, Diyala and Nineveh.

In Kirkuk, jihadists have killed a dozen village leaders just in the past six months, according to local officials.