Guess which film knocked Prince of Persia off the top spot at the Danish box office this week. Sex and the City 2? Valhalla Rising 3? Wrong: it's a new film called Armadillo, by young Danish director Janus Metz, that has provoked a furious debate in Denmark since its premiere in Cannes last week. The film, its director calculates, has already been the subject of 300 to 400 articles in the Danish press. The Danish minister of defence, Gitte Lillelund Bech, has seen it, as have many other politicians and senior members of the military, who have now commissioned an inquiry into events it shows. There has been such a clamour among the public to see it that the film has been rushed into cinemas this week, almost two months in advance of its original release date.

Armadillo is the name of the "forward operating base" in Helmand province, Afghanistan that is home to 170 Danish and British soldiers. The incident that caused particular consternation comes toward the end of the documentary when the Danish soldiers are caught in a firefight with the Taliban. The soldiers are exhilarated after they finally kill their adversaries. What has shocked Danish public opinion is the suggestion (as one soldier later puts it) that they "liquidated wounded people and piled up the dead to take pictures of ourselves as heroes".

Armadillo doesn't offer conclusive proof that the Danish soldiers broke the rules of engagement. Nonetheless, the very possibility that they might have done is startling in itself. The public has been shocked by the level of brutality shown by Metz. The notion that the Danes are in Afghanistan on a peacekeeping mission and spend their days building schools and "giving out candy to kids" is clearly no longer tenable.What really happened when the Taliban in the ditch were killed is unlikely ever to be unravelled. Says Metz: "It was my intention to place the viewer in a position where he could say that it's not even possible to know what was going on. Maybe the soldiers don't even know themselves."

Metz says he grew very close to the soldiers he was filming. "The whole question of embeddedness carries this paradox. You become 'one of them', lose your critical perspective and start becoming a soldier yourself. But you have to step back and be able to describe." Metz says he was "not out to expose the soldiers, or pull their pants down." He simply set out to be as honest as possible about their experiences. "When you manage to defeat your enemy, there is great relief and great exhilaration. Maybe we're looking at something that goes to the core of something very human," Metz says. "The soldiers are so close to death and they actually kill someone. The way they handle the bodies afterwards maybe testifies to something at the very core of humanity – of our grubby human nature. War has always been there. It has always been part of us."

Armadillo has many of the hallmarks of fictional war movies. We see the young soldiers at home in Denmark, preparing to go to the front for the first time. In Afghanistan itself, they watch porn on laptops while on night duty, and relish the camaraderie of being part of a tight-knit platoon. However, their bravado is soon undermined. During a firefight, one doe-eyed young soldier is wounded. His baffled, mud-encrusted face makes it very clear that this isn't just paintball. At the same time, Metz also tries to show the experience of the Afghans themselves. He highlights the plight of farmers caught between western soldiers (with guns) and Taliban insurgents (also with guns). These farmers have to cope as their cattle are killed and their crops trampled.

Politicians have reacted to Armadillo as the film-makers expected, and along party lines. "They have used it to argue for their own opinions," producer Ronnie Fridthjof says. "The left wing says, 'Oh, this proves we need to get out of the war'; whereas the right wing say, 'Our boys are doing a really good job!'"

Metz himself refuses to be drawn on the central question of whether the Danish troops should still be in Afghanistan. "I am not really a politician. I am a film-maker preoccupied with film-making questions," he says. "Having said that, I think it's very important that we start taking Afghans more into consideration when we are talking about Afghanistan, and that we start looking more at the history of the country. Many of the Afghans I have spoken to see the international forces as people who've just landed from the moon."