Restrepo: Is this the greatest war film ever?

An exploding roadside bomb sends panic through a routine patrol. A handsome and popular soldier is shot dead in a volley of gunfire. His friend collapses in sobs on hearing the news, and comrades restrain him from rushing to the body. Later, smoking and joking, half-naked tattooed soldiers casually fire rounds of ammo into a dry Afghan valley. They dance and embrace to the Sam Fox classic "Touch Me (I Want Your Body)". No wonder they're calling Restrepo one of the best portrayals of war ever.

It is released in British cinemas this weekend, but the critics have already given it the thumbs up: it scooped the Grand Jury Prize for best documentary at the 2010 Sundance Film Festival, and is being tipped to win best documentary at next year's Oscars. It is Film of the Week in the latest London issue of Time Out, and on the BBC's Kermode and Mayo Film Review show, and has scored an unusually high 97 per cent positive rating on RottenTomatoes.com, considered a barometer for critical opinion.

The film's haunting depiction of life – and death – on the front line brings something new to a century of war and cinema. The difference is that this is fact, not fiction. No script. No acting. No props. Real blood, real bodies. Until the end you don't know which soldiers survive. It is not an easy film to watch, much less forget.

Of course there have been war documentaries before, many of them excellent. The top prize at Cannes in May went to Armadillo, a Danish fly-on-the-wall film shot at a base in Helmand Province last year. But what amazes about Restrepo is the rare access its makers had to US soldiers.

It was created by Vanity Fair journalists Sebastian Junger and Tim Heth -erington, who were embedded for one year of a 15-month deployment of a platoon in the Korengal Valley – prime Taliban country, nicknamed the Valley of Death.

The film, shot between 2007 and 2008, takes its name from the platoon's remote outpost which, in turn, was named by the men in memory of Private Juan Sebastian Restrepo, an early casualty. The Colombian-born medic, who spoke with a lisp and played flamenco guitar, was only 20 when two bullets tore through his throat.

The US military began withdrawing from the Korengal Valley late last year, having lost nearly 50 lives there, and, according to Hetherington, senior military figures have privately expressed alarm at the film's frank portrayal of a soldier's lot: "When the military saw the film, I got the impression they were surprised by the amount of access that we had. It has certainly raised eyebrows within the US military establishment."

In an early scene, with echoes of the Vietnam classic Apocalypse Now, a platoon is dropped into Afghanistan by helicopter, their nervous faces cut with shots of the valley below. The sense of foreboding is summed up by one soldier, who said: "I thought, holy shit, we're not ready for this."

The film is likely to raise fresh concerns about the psychological effects of war on servicemen. Some of the men featured appear at times to be in a state of shock and almost all have needed psychiatric help since their deployment.

The aim of the project was, according to the photographer, to provide a truthful and honest account of their experiences. "We are taking people on a 90-minute deployment. Of course, this is a mediated version, because it is edited down from 160 hours of film, but it's a pretty honest and truthful version."

Confirmation of that has come from the soldiers in the film who have seen it, and have vouched for its truthfulness. It is also proving to be a hit among British servicemen: on Monday, the 2nd Battalion, the Parachute Regiment, was given a private screening at Colchester barracks ahead of their deployment to Helmand two days ago.

Although there is no plot as such, the film inevitably follows a trajectory over the course of the year. Fly-on-the-wall sequences, including real-life battle scenes and tense negotiations with local Afghans, are interspersed with emotionally charged interviews with clearly traumatised soldiers. These interviews have added poignancy, as it is only from these that, as the film progresses, we know who survives.

Last week, Hetherington, who is now based in New York, published a collection of photographs of soldiers sleeping, called Infidel, which attempts to show the humanity of soldiers. "I think soldiers are used as symbols and often misunderstood," he said. "Everyone has seen two- or three-minute network news pieces that really tell you nothing about the war in Afghanistan. You read political op-ed pieces by people who have probably never been out there.

"We made the film because we felt the experience of the soldiers needed to be seen and digested, understood, somehow honoured, as a starting point for a discussion about the war. We have a responsibility back here to to take a bit of time out to understand."

He worries that some troops are too young to grasp the nature of war when they are recruited. "Society puts these men in a group, makes them bond in a brotherhood, and uses that as mechanism by which men will kill and be killed for each other. That's at the heart of the war machine, not the images that are represented. Does a young guy aged 18 really know what he's letting himself in for? The state sanctions young men as an instrument of violence, and all I'm asking for is that we have an honest reflection on that."

A former photographer for The Independent, he describes himself as a liberal journalist, but is at pains to stress the film's neutrality. Indeed, he makes the point that, since the 2001 invasion, there have been fewer civilian casualties in Afghanistan than in each of the two preceding decades. "According to Human Rights Watch, there have been 19,000 civilian casualties since 2001, and the uppermost estimate is 30,000. That's an awful lot of innocent people killed. But that's nothing compared to the 400,000 who died in the 1990s when the Afghan warlords and the Taliban fought it out. And it's nothing compared to the decade previously, when over a million people died."

Making the film has altered his impression of soldiers and he hopes it can change ours too. "It took time to earn their trust but I'm good friends with a lot of them now. We went through some really intense stuff." He said the relationship between the press and the military has always – rightly – been prickly, though he is concerned for the future of war-reporting. A rumour is going around that the Ministry of Defence is now to cut down on the number of journalists it allows to be embedded, and seeing Restrepo, you can understand why that might be true.

A MoD spokesman later flatly denies this allegation, but to watch the crumpled and sobbing figure of Sergeant John Kennard react to the death of his friend Sergeant Rougle during a deadly ambush is to see the uncomfortable side of war.

Knowing this is a real experience, and he is not an actor, makes it all the more traumatic: it's hard to imagine anyone keeping a camera rolling when faced with this. "Yes, it was upsetting, and it's difficult. The American lines had been overrun by insurgents, people were being killed at close range, and we were in a state of shock. But you have to go on to autopilot. I was just doing my job."

Five great war documentaries

'Standard Operating Procedure' (2008)

Director Errol Morris examines the torture of suspects at the hands of US military police in 2003 at the infamous Abu Ghraib prison in Iraq. Morris says that his intent was "not to say that these 'bad apples' were blameless... but that they were scapegoats."

'The Fog of War' (2003)

Subtitled "Eleven Lessons from the Life of Robert S McNamara", Errol Morris, again, uses archive footage, recordings of US government members, and an interview with former US defense secretary McNamara, aged 85, to examine the nature and conduct of modern war.

'The Sorrow and the Pity' (1969)

French documentary from Marcel Ophüls, looking at the Vichy government's dealings with the Nazis. Ophüls used archive footage and interviews with a German officer, collaborators, and resistance fighters.

'Armadillo' (2010)

Danish film examining the war in Afghanistan. Janus Metz's film follows young troops on their first mission in Helmand and premiered at this year's Cannes Film Festival.

'Brothers at War' (2009)

Intimate portrait of director Jake Rademacher's bid to understand the sacrifice and motivation of his two brothers serving with US forces in Iraq.