The strike on Friday near Iraqi Kurdistan's second city Sulaimaniyah came as Kurdish authorities in neighbouring Syria said a drone attack also by Turkey had killed four members of the Syrian Democratic Forces (SDF).

Ankara and its Western allies classify the PKK as a "terrorist" organisation. Turkey also considers the main component of the SDF, the People's Protection Units (YPG), to be a "terrorist" offshoot of the PKK.

The Turkish army rarely comments on its strikes in Iraq, but routinely targets PKK rear bases in the mountains of the Kurdistan region.

On Friday around 8:00 pm (1700 GMT), "four PKK fighters were killed and another wounded when a Turkish army drone targeted their vehicle near the village of Rangina" north of Sulaimaniyah, according to a statement from Iraqi Kurdistan's anti-terrorism services.

Since 1984 the PKK has waged an insurgency in Turkey that has claimed tens of thousands of lives, and Ankara has long maintained military positions inside northern Iraq where it regularly launches operations against them.

Two raids a week apart in May in Iraqi Kurdistan's Sinjar district killed six Yazidi fighters affiliated with the PKK, in strikes local security officials blamed on Ankara.

In late February and early March, strikes which the anti-terrorism service attributed to Turkey, again killed fighters from the Sinjar Resistance Units. The movement 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.

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

On Tuesday the office of Iraqi Prime Minister Mohammed Shia al-Sudani referred to an "upcoming visit" by Turkey's President Recep Tayyip Erdogan, but did not provide a specific date.

The meeting would likely focus on economic activity as well as the sensitive issue of water.

Baghdad says upstream dams built by Turkey on major rivers it shares with drought-hit Iraq have contributed to severe water shortages in recent years.