Iraqi Kurdish peshmerga fighters were killed. AP
The Saturday evening bombing south of the city of Sulaimaniyah underlined the "serious threat" IS still poses to the Kurdistan region four years after the Iraqi government declared victory over the jihadists, the region's prime minister Masrour Barzani said.
The region's peshmerga ministry said the slain fighters who were hit had been on their way to reinforce comrades who had come under attack by IS fighters.
"We have warned time and again about the dangers posed by the Islamic State group terrorists," Barzani said.
The last major attack blamed on IS in Iraq was an assault on a checkpoint south of Kirkuk that killed 13 policemen in September.
The last major attack claimed by IS was a July bombing in the Baghdad Shiite district of Sadr City, which killed 30 people.
IS seized swathes of Iraq in a lightning offensive in 2014, before being beaten back by a counter-insurgency campaign supported by a US-led military coalition.
The Iraqi government declared the Sunni extremists defeated in late 2017, but the jihadists retain sleeper cells which continue to strike security forces with hit-and-run attacks.