The AS350 Eurocopter crashed in the district of Chamanke in Dohuk province in Iraq's semi-autonomous Kurdish region the previous night, the counterterrorism service said in a statement posted on social media. All of its passengers were killed, the statement said.

An investigator at the scene of the crash said at least seven were on board. The person spoke on condition of anonymity because they were not authorized to brief the media while the investigation is ongoing.

The helicopter was carrying militants belonging to the outlawed Kurdistan Worker's Party, or PKK, the statement said. The incident is shrouded in mystery because no party has yet claimed ownership of the military helicopter.

The Iraqi government, the U.S-led coalition, and Turkey had been contacted by the Iraqi Kurdish regional government about the crash, but each party denied the helicopter was theirs, the statement said.

Zagros Hiwa, a PKK spokesperson, said the group does not possess helicopters and they were also investigating the incident. He also cast doubt on the presence of PKK militants onboard the flight, saying they may have a coalition helicopter carrying fighters with the People’s Protection Units, or YPG, another PKK affiliate active in Syria.

A spokesman for the U.S.-led coalition declined to comment, saying the crash fell outside the scope of the coalition's operations.

Turkish defense ministry officials said that initial reports that the helicopter had been Turkish were “completely untrue” and that there was no helicopter flight belonging to the Turkish military in the region.

The PKK has been waging an insurgency against Turkey since the 1980s and is considered a terror group by Ankara, the United States, and the European Union.

The PKK militants have established safe havens in northern Iraq and roam freely there and frequently come under attack by Turkey.