File photo shows Polish-born French director Roman Polanski as he arrives for the American Foundation for AIDS Research (AMFAR) "Cinema Against AIDS" benefit in Le Moulin de Mougins. (GERARD JULIEN/AFP)

GENEVA, October 20, 2009 (AFP) - Switzerland's top criminal court refused Tuesday to release Oscar-winning director Roman Polanski from jail on bail, saying there was a "high" risk that he could flee the country.

Polanski had asked the court to free him while Switzerland decides whether to extradite him to the United States, which had issued an arrest warrant over a three-decades-old child sex case.

"The Swiss Federal Criminal Court has rejected Roman Polanski's appeal against detention pending extradition," the court said in a statement.

"The court considered the risk that Roman Polanski might flee if released from custody as high," it added.

The director of "Rosemary's Baby", "Chinatown" and "The Pianist" has been regarded as a fugitive by US authorities since he fled the United States in 1978 after admitting to having sex with a 13-year-old girl.

He was detained by Swiss police acting on a US extradition warrant when he went to Zurich to collect an award at the city's film festival last month.

"According to Swiss law, detention is the rule during the entire extradition proceedings," said the court.

Polanski's French lawyer said he would appeal to the Swiss supreme court.

The 76-year-old film-maker had put up his chalet in the glitzy Swiss ski resort of Gstaad as bail, according to court documents.

His lawyers have also argued that given his age and in view of his two children who are still in school, Polanski would not put at risk over half of his assets by escaping.

Polanski was admitted to hospital over the weekend for medical tests, and was due to be returned to prison.

However, Switzerland's federal criminal court assessed that the bail was not in line with requirements set by the law.

Highlighting the high risk of flight, the court noted Polanski's dual French and Polish nationalities, and pointed out he could travel across the borderless Schengen zone "without problem and without travel documents."

He could also leave the country using a private plane or helicopter, said the court.

"In view of the circumstances, that the appellant can practically leave the country in a matter of hours from any point in Switzerland and in particular to escape to France, even a requirement for him to report daily to the police would be unable to effectively prevent an escape," it said in its ruling.Polanski's French lawyer, Herve Temime, said he would appeal to the supreme court.

"We will try to provide even stronger and more suitable guarantees," Temime said. "We will seek to demonstrate that there is no risk in ordering Roman Polanski's release."

The decision by the criminal court was in line with the Swiss justice ministry's decision on October 6 to oppose bail for the film-maker.

Justice ministry spokesman Folco Galli told AFP then that authorities felt there was a "great danger" that Polanski would escape pending a full extradition request from the United States.

Under an extradition treaty with the United States, prosecutors in California have 40 days from the time of Polanski's arrest to lodge their full extradition request, which the court will subsequently rule on as well.

Polanski's arrest had sparked an uproar in the cinema world, with top US film-makers including Woody Allen, David Lynch and Martin Scorsese among the first to sign a petition for his release.

On Thursday, French President Nicolas Sarkozy criticised the US warrant, saying it was "not a good administration of justice."

"I understand that people are shocked by the gravity of the accusations against Roman Polanski," he told Le Figaro newspaper.

"But I add that it is not a good administration of justice to do this 32 years after the facts when the person concerned is today 76 years old."