Nine Syrian Democratic Forces (SDF) fighters, including one of their commanders, were killed this week when two helicopters crashed in bad weather in northern Iraq, the Syrian Kurdish-dominated coalition, allies of the USA.

Authorities in the autonomous Iraqi Kurdistan region said on Thursday that at least five people were killed in a helicopter crash in the region, noting that some of the victims were members of the Kurdistan Workers’ Party (PKK), which is considered a “terrorist organization” by Turkey and its Western allies.

The PKK did not confirm the information and the causes of the accident were not specified.

According to the SDF, two helicopters carrying members of its anti-terrorist unit in Sulaymaniyeh, Iraqi Kurdistan, crashed due to bad weather. Among the victims was the SDF’s counter-terrorism chief, Servan Kobani.

The delegation was traveling to Iraqi Kurdistan “to exchange information at the military and security level,” the statement added.

The SDF has been at the forefront of the fight against Islamic State jihadists in Syria. They are the de facto army of the Kurdish administration in the Kurdish-controlled areas of northeastern Syria. Turkey characterizes the main component of the SDF, the YPG (People’s Protection Units), as a “terrorist” organization, considering it an offshoot of the PKK.