Three Dutch bikers from the No Surrender gang have traveled to northern Iraq to join the fight against the Islamic State.
Pictures on social media suggested that the ex-servicemen have entered the country on the side of the Kurds, with one posted image showing a man making the "victory" sign inside a bunker. Their presence near Mosul has now been confirmed.
The caption on this tweet reads" "Ron from The Netherlands has joined the Kurds to exterminate the rodents of [ISIS]."
There was a question that the three men might face criminal charges upon their return. However, the Dutch government confirmed on Tuesday that this is untrue.
Public prosecutor spokesman Wim de Bruin told AFP: "Joining a foreign armed force was previously punishable, now it's no longer forbidden. You just can't join a fight against the Netherlands."
Participating in terrorism, or in terrorist designated groups such as the Islamic State, is still illegal for Dutch citizens. De Bruin added: "That means that even preparing to join IS is punishable."
Dutch people are not allowed to join the Kurdistan Workers' Party either, as it is also classified as a terrorist organization by the Netherlands, among other countries.
"Dutch citizens fighting on the Kurdish side would of course be liable to prosecution if they committed crimes such as torture or rape," de Bruin told AFP. "But this is also happening a long way away and so it'll be very difficult to prove."
No Surrender is one of the biggest motorcycle gangs in the Netherlands. On their official website they list 33 chapters, including divisions in Spain, Germany, and Turkey.
No Surrender's leader Klaas Otto told Dutch broadcaster NOS that the members who travelled to Mosul were from Amsterdam, Rotterdam, and Breda, and that they had decided to go after seeing images of the beheadings. He added that they weren't traveling as representatives of the motorcycle gang: "It's a private matter. They themselves have made the choice."
Otto also told broadcaster Omroep Brabant that, as ex-servicemen, they were well qualified for the task. "They are trained guys with lots of experience. Also with foreign missions. They are extremely disciplined, they do not drink alcohol, not even on club nights."
The Netherlands has a small Kurdish population of an estimated 70,000 people.
Follow Sally Hayden on Twitter: @sallyhayd