ISIL on Saturday killed two policemen guarding a northern Iraqi oilfield, in a first attack on energy facilities since the extremists were driven from the region's towns, a security source said.
"A large number of ISIL terrorists attacked a post of the oil police force near well 43 in the Khabbaz oilfield, killing two and wounding a third," the source said.
Iraqi forces announced the total defeat of ISIL in the country in December after a punishing campaign to oust the group from territory it seized in 2014.
But cells of the extremist group remain behind and have continued to carry out bloody attacks, including killing 27 pro-government fighters in an ambush in the Hawija region last week.
Iraq's central government retook the vital oilfields around Kirkuk from the autonomous Kurdistan region last year after it held a disputed vote on independence.
The income from oil is vital for Iraq, OPEC's second biggest producer, as the country needs tens of billions of dollar to rebuild after the devastating fight against ISIL.