Three more fighters were wounded, said the counter-terrorism service of the Kurdish region where fighting has often flared between the Turkish army and the PKK.

Around 5:00 am (0200 GMT) "a Turkish army drone targeted a headquarters of the Sinjar Resistance Units," the service said, referring to an armed group operating in the mainly Yazidi Sinjar district which has ties to the PKK.

"Three fighters were killed," the statement added.

The PKK has been waging a deadly insurgency against the Turkish state for four decades and the conflict has repeatedly spilt across the border into northern Iraq.

A bombing raid in Sinjar district a week ago killed three fighters.

The Turkish army rarely comments on its strikes in Iraq but routinely conducts land and air military operations against PKK rear-bases in autonomous Kurdistan as well as Sinjar district.

Strikes attributed to Turkey in late February and early March also killed fighters from the Sinjar Resistance Units, a movement that took up arms against the Islamic State group in 2014 following the jihadists' massacre of thousands of Yazidi men and their abduction of thousands of women for use as sex slaves.

The Yazidis follow a pre-Islamic faith, that is anathema to the Sunni Muslim extremists of IS.

Illustrating the complexity of the security situation in northern Iraq, the Sinjar Resistance Units are also affiliated with Iraq's Hashed al-Shaabi (Popular Mobilisation) force, a pro-Iranian former paramilitary group now integrated into the regular armed forces.

Ankara has set up dozens of military bases in Iraqi Kurdistan over the past 25 years to fight against the PKK, which it and its Western allies consider a terrorist group.

Both the federal authorities and the Kurdistan regional government have been accused of tolerating Turkey's military activities to preserve their close economic ties.

Tensions erupted on Saturday around northern Iraq's Makhmur camp, which shelters Kurdish refugees from Turkey.

Officials said the Iraqi army planned to build a perimeter fence to control all movements in and out of the camp, which Ankara considers a recruitment ground for PKK militants.