It's hard to describe the best bit in Sylvester Stallone's new Burma-set Rambo movie, cleverly titled Rambo. It could be the bit where the local tribesmen are forced to walk through a live minefield and are blown to bloody shreds. Or it could be the bit where the soldier's head is imploded by a point-blank revolver round. Or the bit when the children are shot and tossed alive into a fire, or when the nasty boy-raping commander is disembowelled, or when the entire Burmese battalion gets pulverised into a meaningless bloody mass by an enormous machinegun that's neatly wielded by our titular hero.

No, in fact the best bit of Rambo is the stunningly audacious way in which all concerned with the production have justified its hyperviolent excesses in terms of contemporary politics. “We've done our research and we're not making this up,” Kevin King, the film's producer, claims when defending Rambo's paper-thin narrative. It focuses on our hero's bloodthirsty attempts to defend the country's Karen tribespeople from a genocidal Burmese military. “It's all factual, documented, not violence for violence's sake. For 60 years these people have been systematically annihilated and nobody knows it. Nobody knows how horrific it truly is.”

“We did tons and tons of research,” adds Stallone himself, speaking ex cathedra from the comfort of the Dorchester hotel in London this week. “There's an unbelievable amount of material out there, literally hour by hour. It's almost a teletype of the horrendous things that are going on there. And it's hard to believe that it's publicised and nobody does anything about it.”

And yet, hang on, this is a Rambo movie! It's not Syriana, nor is it a John Pilger polemic. It's a film about a lonely guy with big muscles and an even bigger gun who shoots people to make himself feel better. It's surely a reflection of today's geopolitical urgencies that even a movie as dumb as Rambo feels the need to lacquer itself in foreign-policy rhetoric. The results make for uncomfortable viewing - an opening newsreel montage of Burmese atrocities followed closely by a shot of Stallone, beefed-up and immobile in his Rambo bandana, is a telling indicator of the project's malformed political logic.

Worse still, the movie has taken the grisly tenor of these atrocities and inserted it into the normally cartoonish violence that defines the franchise. Thus we're treated to depictions of casual limb-lopping, child murder and the most obscene disregard for human life. All of which is ultimately used not to score political points, but as plot motivation for Rambo's inevitable revenge. It's like Schindler's List played for thrills, or Saving Private Ryan for PlayStation junkies.

Again, Stallone is on the defensive. “I don't think this film is horrific and bloody, because that's what war is. It's not gratuitous violence. Gratuitous violence is a guy dressed up in a fright wig with a meat cleaver, chasing teenagers around the woods for ten hours. This is war, and it's a civil war - which, as you know, is by far the most vicious of all wars.”

It wasn't always like this. When Rambo began, he was a bracing new action star, the central character of a 1972 novel by David Morrell that was adapted for the screen by Stallone himself in the 1982 movie First Blood. In that landmark film John J.Rambo refuses to kill and instead destroys a small Midwestern town, terrifies some part-time soldiers and laments the fate of disenfranchised Vietnam veterans. Stallone, still hot from his double-Oscar nominations for Rocky (as writer and actor), was a revelation in the role, and a remarkable combination of soft soulful eyes, hangdog demeanour, and the ruthless Dirty Harry machismo that was then in vogue.

When the bellicose sequel, Rambo: First Blood Part II, arrived three years later, it became a box-office behemoth and a cultural landmark, forever tied to the hardline anti-Soviet policies of Ronald Reagan (who was subsequently parodied in the press as “Ronbo”). The film, co-written by James Cameron (Titanic), allowed Rambo to return to Vietnam and settle some old scores. It was, even by Stallone's standards, a cartoon fantasy. “Rambo was a complete American dream,” he says today. “It had nothing to do with reality.” By the time Stallone had served up his Commie-bashing Afghani adventure, Rambo III (which is technically Rambo II: First Blood Part III), the public appetite for supermachismo had clearly abated - at the US box office the movie grossed only $53 million on a production budget of $58 million. Stallone, however, blames perestroika for the failure of Rambo III. “Two weeks before the film comes out Gorbachev comes over and gives Reagan a hug, kisses Nancy on the cheek and now I'm a Red-baiter!”

Since then, of course, baby-booming nostalgia has flourished, and affection for Eighties icons such as Rambo has grown, as indeed has affection for Stallone himself (witness the standing ovation he received at Sunday's Bafta awards). The 61-year-old actor proved that he had a light touch when he reinvented his other alter ego, Rocky, in Rocky Balboa in 2006. Here, by focusing almost entirely on the boxer's shattered dreams, he laid a veil of poignancy over a franchise that had become known for bullish triumphalism.

Indeed, there was something ineffably moving in the desperation of a character, lumbering and careworn with age, who pleads to his son for understanding in the near mythic line: “What's so crazy about standing toe to toe with someone and saying, ‘I am!'?”

With the reinvented Rambo, however, Stallone has miscalculated badly. He says that, first, he wanted to go back to the 1980s and thus reintroduce a modern audience to an old-style hero. “Back then it was pretty simple,” he says. “It was like mano-a-mano, who kills who first? I thought that would be interesting, because an entire generation hasn't seen Rambo. They haven't seen the kind of old-school meet-you-at-high noon modern western that it is. Where there's nothing fancy about it, and whoever's the bigger savage wins.”

But his initial entertainment impulse has been hamstrung by lofty ambitions and a depiction of Burmese realpolitik that has subsequently turned Rambo into a 90-minute assemblage of gore-porn.

Audiences who come to whoop and cheer at their tooled-up hero will be in for a strangely brutalising experience. Certainly the audience I watched it with, 200 strong and mostly male, were wilfully determined to mine the movie for nostalgic hits, despite the ostensible subject matter.

Thus they cheered when the Burmese villagers popped like blood balloons, they cackled when Burmese soldiers lost their limbs and they gurgled appreciatively when Rambo finally stepped behind his genocidal supergun and laid waste to a throng of Burmese nasties.

It was a creepy night out, like being a witness to the last days of the Weimar Republic, or a spectator at the Roman Colosseum. And it clearly wasn't entertainment. Even with the best bits.

Rambo is out on February 22

Rambo's enemies: sadists and foreigners

FIRST BLOOD (1982)

Villain: Portly smalltown sheriff Will Teasle (Brian Dennehy).

Distinguishing features: Dislikes drifters with long hair. Likes cowboy hats and good ole boys.

Says: “What possessed God in Heaven to make a man like Rambo.”

Sticky end? Falls through the skylight of the county jail and is forced to listen to Rambo crying.

RAMBO: FIRST BLOOD PART II (1985)

Villain: Torture-loving Russian Lieutenant Colonel Podovsky (Steven Berkoff).

Features: Wears fetching grey jumpsuit. Speaks, strangely, with German accent.

Says: “I see you are no stranger to pain, hmmm?”

Sticky end? Death by rocket- propelled grenade, fired by Rambo from the cockpit of a stricken helicopter. Naturally.

RAMBO III (1988, pictured)

Villain: Genocidal Russian Colonel Zaysen (Marc de Jonge).

Features: Kidnaps Rambo's boss and mentor, Colonel Trautman (Richard Crenna). Hates Afghan rebels. Speaks with thick Russian accent.

Says: “Thees eees your last varning. I wish to teeek you beck alive.”

Sticky end? His helicopter is smashed by Rambo in a Russian tank.

RAMBO (2008)

Villain: Hateful Burmese Major Tint (Muang Muang Khin)

Features: Wears mirrored shades. Likes torture. Rapes young boys.

Says: Not a lot.

Sticky end? What do you think?

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