The Kurdistan Workers Party (PKK) -- which Ankara considers a terrorist organisation -- told AFP it was "investigating" the crash, without confirming or denying deaths among its ranks or whether the helicopter belonged to them.

The aircraft, a Eurocopter AS350, crashed on Wednesday evening in Dohuk province in Iraq's autonomous Kurdistan region, "killing all passengers", Kurdish counter-terrorism services said.

Lawk Ghafuri, the head of foreign media relations in the Kurdistan regional government, tweeted that "at least five passengers of the helicopter" had been killed.

"Investigations are ongoing... to determine the ownership of the helicopter and causes of the incident," he added.

"Some of the passengers who were killed during the incident were PKK members according to initial investigations," he told AFP.

The PKK has a presence in Iraq's Kurdistan region, which Turkey has repeatedly sought to root out in air and ground operations.

In early March, a Turkish drone strike in northern Iraq killed two Yazidi fighters affiliated with the PKK, days after a similar strike killed three other fighters.

The rebel group had waged a brutal insurgency in Turkey that claimed thousands of lives since 1984.