Shy young actor and musician Michael Pitt portrays a Kurt Cobain-like character who is contemplating suicide with smouldering, hypnotic intensity in Gus van Sant's "Last Days".

Movies celebrating - or exploiting - singers who died young generally follow the subject from obscurity to fame to untimely demise. Gus Van Sant's Last Days breaks all the rules of the genre, beginning at the end and never lapsing into flashback as it draws an impressionistic picture of a strung-out, barely coherent rock star before he takes his own life.

Its inspiration is Kurt Cobain, who killed himself in 1994 at the height of his fame, and it is described as "a fictional meditation designed for individual interpretation". It proves just as demanding as that suggests.

When Cobain died in April 1994, Van Sant, who had met him once, had not recovered from the shock registered by the death seven months earlier of River Phoenix, who had been a close friend since he directed him in My Own Private Idaho. Van Sant was developing his ideas for Last Days in 1997 when he met Michael Pitt, and felt he might be suitable for the central role. When the film finally went into production in May last year, Pitt played the lead with a smouldering, hypnotic intensity.

"When Gus told me about the project, I jumped up and told him he had to make this film," says Pitt, an adventurous young actor who is engagingly shy off-screen. "When Gus told me he was considering using me for the character, I just laughed and told him he was crazy. But, from there, we talked about the project over and over again, and it got more and more real. The idea that it was based on Kurt Cobain was the main reason I wanted the film to be made, but it was also the main reason why I didn't want to be involved."

Pitt, who turned 24 last April, says he was much too young to appreciate Cobain's music when the Nirvana star was still alive. "I got to know his music after his death. Unfortunately, when a band gets really big, they have a lot of fans and some don't represent them well. When I was growing up, everyone was a Nirvana fan and everyone knew one song, so I never checked them out at the time."

The whole film was improvised, Pitt says. "We had a kind of map that ran to around 14 pages with the basic outline. For the opening scene it read, 'Blake walks through the forest'. When we got to the forest we figured out what we would do. It felt very free to work that way. Everything was very loose."

Pitt insists that while Cobain was the basis of the movie, it's not based on facts. "I used him as a model, so I used his posture, his speech, his image and what I thought he would be thinking at the time, and from that I created the character."

Pitt spends most of the movie alone on screen in a withdrawn, internal performance. "I just tried to concentrate and stay in the character," he says. "A lot of actors only feel good when they're animated and moving around - when they're crying or puking or whatever. To me, that's the easiest thing to do because it's more external.

"I feel that if you get a person who is very smart and artistic for their environment, and if the community around them isn't taking care of them, bad things can happen sometimes. I've had friends who committed suicide, and when that happens, it feels to me and everyone else in that person's close community of friends that we've failed the person in some way because we let them go. There's something strange and sinister about suicide. It's a human thing. It doesn't happen in the animal world."

Pitt describes working on the film as a dream fulfilled. "I had never worked that way before and I never felt so happy and excited going to work every day. It was very hard work, but when it ended, I just went up to this barn on the set and I wrote Gus a note thanking him for everything and telling him what a special experience it had been for me."

In another departure from the rock biopic rules, there isn't much music in Last Days, and nothing from Nirvana. The soundtrack includes the Velvet Underground classic, Venus in Furs, and most unexpectedly, a Boys II Men promo playing on TV, along with two songs performed by Pitt - an improvised jam using several instruments and his own brooding composition, Death By Birth.

"What you see is what happens," Pitt says. "I had a lot of fears about playing my own music. It wasn't something I wanted to do. I didn't want it to seem that I was using the film to try to publicise my music."

Pitt has his own band, Pagoda, and he brought them to Cannes, where Last Days had its world premiere in May, and they played at the post-screening party. "We were asked to do three or four songs, and when we got there and saw there was such a big crowd, we knew we couldn't just do three songs and leave. So we did a 40-minute set, all our own material. We've recorded an album, which we're thinking of calling The House of Worship.

"From the time I picked up a guitar, music has always been very important to me. I started very late. I bought my first guitar when I was 18, and I paid for it with my first film job, which was a horrible TV show. I got off the plane and they gave me about 400 bucks. I asked what it was for and they said it was for food, a per diem. I walked to the music shop and bought a guitar and taught myself to play it."

Pitt, who was born and raised in New Jersey, did not have acting or music in his family background. "My dad works as a car mechanic," he says, "and my mother is unemployed now, but she used to work for my grandfather, selling clothes and stuff."

He dropped out of school when he was 16 and moved to Manhattan, working in low-paid jobs and taking an acting course. "I did that first TV show because I was starting out," he says. "People didn't know who I was, and I wasn't in a position to choose. It was a job and I didn't have any money. As soon as I finished the show, I got offered Hedwig and the Angry Inch, which was perfect for me.

"People told me I'd never work again if I did that, and they were giving me a lot of American teen movies. It was a weird time for me. I wanted to act, but those teen movies were not what I wanted to do. I turned down a lot of them then. Now I just don't read them if they're sent to me."

Hedwig and the Angry Inch was a brash, inventive and touching musical that attracted critical kudos and a cult following. Pitt's striking portrayal of the Judas figure - Tommy Gnosis, who steals the songs of the transsexual Hedwig and becomes a rock star - brought him several offers he couldn't refuse.

These notably included Larry Clark's Bully, Barbet Schroeder's Murder By Numbers, and Bernardo Bertolucci's The Dreamers, in which Pitt played a naive US student discovering movies, sex and politics during the turbulent events of May 1968 in Paris. Bertolucci picked Pitt when Jake Gyllenhaal turned down the role because of the frontal nudity it entailed, and those scenes led to protracted negotiations with the ratings board in the US.

"That's actually one of the reasons I was interested in doing The Dreamers," Pitt says. "Doing that nudity in the film was definitely a choice. It was not about me wanting to show myself off naked, but more about the fact that you can film the rape of a woman and blow her head off with a gun, and you get an R rating in America. But you can't show the anatomy, whether in a sexual or non-sexual context. That is so wrong. It has a lot to do with what's wrong with America.

"That movie was an amazing time for me. I learned so much. I'm basically a working-class guy and I grew up in an environment in New Jersey where people never went to Paris or Europe in their lifetime. I knew nothing about what happened there in May '68, but I had the best teachers. Bertolucci and a lot of the people on the set were there and experienced it.

"The more films I make the more I learn about technique, and I want to direct some day. I've got a few projects I'm working on. But I also feel music is more for a younger person, so I feel that if I want to givemore time to music, I should do it now and think about directing when I get older, although I would love to do that now."