Lilya 4-Ever (18) ***

Here is the latest from one of cinema's great young directors, a film that showcases an exquisite handling of tone, an uncompromising engagement with its subject and a central performance that balances charm with disquieting credibility.

I saw it last week, and its emotional impact reverberated right through the Easter weekend: Christ's passion had found a vivid modern analogue. Thus Lukas Moodysson's Lilya 4-Ever, a film that everyone should see and yet, conversely, an experience I couldn't wish on anyone. It is the polar opposite of a fun night out.

The poster photograph for Moodysson's previous film Together featured a man's face twisted in the pained rictus of a howl, and made one fear the worst. But its account of a commune in Seventies Stockholm turned out to be a gently satirical comedy of hippie manners, and the poster's howling man would happily recover both his senses and his sobriety. Most of the promotional material for Lilya 4-Ever features teenage children gaily horsing around, and its title, too, suggests an adolescent insouciance, words to be doodled on an exercise book or carved on a bench. Entirely misleading, I'm afraid. The film seems to have been made almost as a rebuke to the sunny, forgiving spirit of Together. It couldn't be less like Together if they'd called it Apart.

Soundtracked by a crazed blast of Gothic rock – "Mein Herz Brennt" by Rammstein, it says here – its opening sequence follows a battered young girl as she limps through a faceless inner city, her destination a foot bridge over a motorway. How she has arrived at this pass constitutes the film's story. The girl, Lilya (Oksana Akinshina), is 16 and not that sweet, but then who would be with a life like hers? Abandoned by her mother, who has just relocated to the States, Lilya must cope as best she can around their dismal housing estate somewhere in the former Soviet Union. Her aunt, a vile old hag, kicks her out of the family apartment, advising her to do as her mother did: "Go into town and spread your legs." Every day Lilya checks the mailbox, hoping for word from her mother, but none arrives.

Sickeningly, inexorably, those who should help Lilya instead betray her. First her mother and her aunt, then her teacher and her friend Natasha (Elina Beninson) turn a cold shoulder. Why? What has she done to deserve such unkindness? Moodysson doesn't presume to provide answers; he simply observes the unfolding tragedy. It is hard to imagine a more poignant image of the girl, kneeling in the mud she slipped in while trying to call her mother back (a dog then trots over and gives her a sympathetic sniff). Even now, though, one senses that there will be worse to follow. Her only friend in the world turns out to be Volodya (Artyom Bogucharskij), a fellow waif who has been kicked out of his home and seeks shelter in Lilya's dank, dreadful flat. "No funny stuff," she warns him as they bed down for the night on a stained mattress. No funny stuff: we will remember this phrase afterwards with a shudder.

The idea of children pulling together against the neglect or abuse of the supposed grown-ups also runs through Together and Moodysson's earlier feature Show Me Love. Children are obliged to become wise before their time simply because adults can't be relied upon. Lilya begins to turn tricks, sacrificing the last of her childhood in order to survive; in spangly top and eyeliner she looks far too young for the hooker's life, but what happens later brutally strips away that illusion. At one point she thinks she has met her saviour, a friendly young man named Andrei (Pavel Ponomarev) who promises her a life of prosperity across the Baltic Sea in Sweden – they have jobs there! For a while we are as keen to believe Andrei as Lilya is.

By degrees our hope trickles away, and what Lilya finds in the drab precincts of Malmo is infinitely worse than the life she has left behind. Close-ups of pale men, faces sweaty and contorted, loom horribly over the lens: Moodysson uses his camera so that we see these fleshy transactions from Lilya's point of view, until the faces blur into a long, grotesque montage.

So how keen are you to see this tale of raped innocence? How much do you want to know about the squalor of human trafficking? Moodysson introduces a supernal element late in the story that mitigates the agony, but only a little. When you have been through what Lilya has, the appearance of a guardian angel who tells you, "This world isn't that good" feels pretty redundant. Oblivion seems a blessed release. Lilya 4-Ever is a film to dread in advance, and to flinch at in duration.

Nevertheless, and this is the curious part, I felt glad to have seen it. For one thing, I wouldn't want to have missed Oksana Akinshina and Artyom Bogucharskij as the modern Hansel and Gretel, preyed upon by witches and devils, yet still capable of love while they have each other. It feels somehow typical of Lilya that the first thing she buys with her trick money is a basketball for Volodya, whose astonishment suggests that no one has given him anything, ever. Cherish that moment – there are few such in Lilya 4-Ever.