URICH?Roman Polanski's lawyers on Monday vowed to fight his extradition to the United States over a three-decade-old child sex case and called his surprise detention in Switzerland "illegal".

Support from the movie industry for the 76-year-old Polish-French film director also grew as top film directors declared themselves "astonished" at his arrest for the 1977 case.

"Filmmakers in France, in Europe, in the United States and around the world are dismayed by this decision," said a petition organized by SACD, which represents performance and visual artists.

"It seems inadmissible to them that an international cultural event, paying homage to one of the greatest contemporary film-makers, is used by police to apprehend him."

French Foreign Minister Bernard Kouchner said the case was a "bit sinister" and that he had asked the United States to drop the charges. A Swiss newspaper said the country should be "ashamed" of the "trap" it laid for the Oscar-winning director.

Polanski, who achieved international acclaim for movies such as "Rosemary's Baby", "Chinatown" and "The Pianist", was detained as he arrived on Saturday to receive a lifetime achievement award at the Zurich film festival.

Swiss authorities said they were awaiting an extradition request from the United States over the case in which he admitted having sex with a 13-year-old girl. The victim has since joined defense lawyers in urging for the case to be dismissed.

Los Angeles prosecutors confirmed Monday they would file a warrant seeking Polanski's return to the United States, noting they had 40 days to prepare it.

"We will prepare an extradition warrant and it will be sent to the Justice and State Department and it will go through the diplomatic channels," Los Angeles County District Attorney spokeswoman Sandi Gibbons said.

But Polanski's French lawyer, Herve Temime, said the director rejected any prospect of extradition.

"Given the extravagant circumstances of his arrest, his Swiss lawyer will ask without delay for him to be released, possibly under certain conditions," a statement from Temime added.

Kouchner said he was working with Polish counterpart Radek Sikorski to help Polanski and that they had jointly written to US Secretary of State Hillary Clinton to ask for the charges to be dropped.

"This affair is frankly a bit sinister. Here is a man of such talent, recognized worldwide, recognized especially in the country where he was arrested. This is not nice at all," Kouchner told France-Inter radio.

But the State Department said Monday it would not wade into the row.

"The role of the Department of State will simply be to review that request, to make sure it meets sufficiency in terms of our extradition treaty with Switzerland," State Department spokesman P.J. Crowley said.

Polanski fled the United States in 1978 before sentencing on a charge of unlawful sexual intercourse with a minor. He has never returned, even missing the Oscar award for "The Pianist" in 2003.

Temine said Polanski visits Switzerland often and owns a chalet in Gstaad where he spent three months this year.

Switzerland says Polanski is being held under an international alert issued by the United States in 2005. As Polanski can launch several appeals, a final extradition decision could take weeks or months, legal experts said.

Swiss Justice Minister Eveline Wildmer-Schlumpf said her country had a duty to act on the US request and there was no political "pressure" involved.

But Swiss newspapers have speculated the government ordered the arrest in a bid to redeem itself with the US government after a row over banking secrecy.

"Switzerland let a guest walk into a nasty trap. We should be ashamed," commented the Blick tabloid.

The French consul general Jean-Luc Faure-Tournaire, who visited Polanski in a Swiss prison on Monday, said he was being well treated.

"Mr Roman Polanski is being well treated. He thanks the many people who have shown support through the press and public opinion," the consulate said in Zurich.

In May, a Los Angeles judge refused Polanski's bid to dismiss the underage sex case after he failed to appear in court.

Polanski's legal team argued the conviction should be annulled because the judge who heard the 1970s case had improperly colluded with prosecutors. The judge has since died.