The contentious new film from American satirical documentary-maker Michael Moore had an emotional international premiere at the Cannes Film Festival yesterday.

The disturbing nature of Sicko, which deals with the failings of the American healthcare system, has been a closely guarded secret until now. It focuses on the suffering caused to the nine million children living in the United States whom Moore says are left without any health cover because of the country's reliance on private insurance. 'We are the last country in the industrialised world to have this system,' the film-maker said after the screening. 'The poorest child in Britain has a longer life expectancy than the average American child.'

Moore's style in this film is less confrontational than in his previous documentaries, Fahrenheit 9/11 and Bowling for Columbine, and he said this was a deliberate move. 'I wanted a different tone. I wanted to show things a different way,' he said. 'I started to think about the whole conceit about the audience living vicariously through someone on screen. This film is a call to action. It is not for Michael Moore to do it, but for the American people to do it.'

Moore said he had his own health cover through his union membership and that since making Sicko he has gone on a diet. 'I am actually a fairly skinny person from the Midwest,' he said. 'But I am eating those things you call fruit and vegetables. Inspired by the film, I have lost about 25 pounds in the last two months.'

The film has received extra publicity after a White House threat to Moore because he filmed part of the movie in Cuba - a place that is officially out of bounds for Americans because of the trade embargo. 'We are under investigation,' explained Moore. 'Ten days ago I received a certified letter from the Bush administration telling me that I was under investigation for violating the US law that inhibits trade or travel to Cuba. I had 20 days to respond and my time is up on Tuesday.'

He said his lawyers are concerned the government might try to confiscate the film or the sequences filmed in Cuba.

Producer Harvey Weinstein said he was backing Moore in defence of the film. 'They are going to sue. We will just get more lawyers.' Weinstein has been here before with Moore. He produced Fahrenheit 9/11 and backed it when parent company Disney was not happy about its release due to its controversial content. Weinstein has since set up his own independent company. 'I am nothing to do with Disney any more, so I don't care about the government,' he said.

Moore, who won the coveted Palme D'or at Cannes with Fahrenheit 9/11, said that those who watch Sicko will see that the provocative trip to Cuba was not part of the plan. In fact, he is shown taking American emergency workers who have untreated health problems to the country. The sick workers had helped at the World Trade Centre on 11 September 2001 and, Moore argued, would have got better care than they were receiving in the US by visiting the Guantanamo Bay US base on the island. He took them there but was turned away and then went to Cuba. 'The point was not to go to Cuba, but to go to American soil which happens to be in Cuba,' said Moore.

He admitted to the assembled world press that the legal dispute has served to draw public attention to his film and said he was at a loss as to why the US government decided to act now. Moore added that he and Weinstein were not yet considering the possibility of the film being confiscated before its American release date on 29 June. 'For that to happen in the United States would be an insane thing,' Moore said.

One of the unlikely stars of the film is Tony Benn. Moore says he first spotted the former Labour cabinet minister on an edition of Question Time on the BBC seven years ago. 'I didn't know who he was, but he spoke about student loans and said it would create a generation of wage slaves with debts. He asked: "Why wouldn't employers want that?" '

The film, its creator insists, is not partisan. 'It is not a Democrat film,' he said. 'They have been bought too.'

His real enemy when he returns to the United States this week will be the health companies and pharmaceutical companies. 'They are not going to like this film and to some extent that might be a far scarier force than the Republicans and George Bush,' he predicted.