Roman Polanski is hoping for help from the world's most powerful man as he battles extradition on a child-sex charge - he has reportedly written to U.S. President Barack Obama.

The Rosemary's Baby director is currently under house arrest in Switzerland as American prosecutors attempt to force him back to the States to face sentencing for having unlawful sex with a 13-year-old girl in 1977.

Several high-profile figures have already spoken out in support of the movie-maker, including Johnny Depp, Pierce Brosnan and Ewan McGregor, and Polanski is now hoping Obama will join them - he has allegedly written to the U.S. President asking to be spared jail.

French magazine L'Express reports the country's leader President Nicolas Sarkozy - who is backing Polanski's bid for freedom - "played the postman" and delivered the hand-written note to Obama earlier this month.

Journalists at the publication wrote, "In an astonishing act of backroom diplomacy, Nicolas Sarkozy hand-delivered a letter from Roman Polanski to Barack Obama last week on the sidelines of the anti-nuclear proliferation summit in Washington."

Polanski fled to France in 1978 after pleading guilty to a charge of unlawful sex with a minor. He was arrested by Swiss officials last September after arriving in the country to attend a film festival in Zurich.