Roman Polanski lost the first round Tuesday in his battle to avoid extradition to the United States for having sex in 1977 with a 13-year-old girl.

Already locked in a Zurich cell for the last dozen days, Polanski learned he will remain incarcerated for an extended period as the Swiss Justice Ministry rejected his plea to be released from custody.

Swiss authorities expressed fear he might flee the country if freed from prison. The director of such film classics as "Rosemary's Baby" and "Chinatown" has been wanted by U.S. authorities since fleeing sentencing 31 years ago.

SLIDESHOW: Roman Polanksi: Anatomy of a Sex Scandal

"We continue to be of the opinion that there is a high risk of flight," said ministry spokesman Folco Galli, explaining the decision.

Galli told The Associated Press that the threat was too great for the government to accept bail or other security measures in exchange for the release of the filmmaker.

Polanski was apprehended Sept. 26 as he arrived in Zurich to receive an award from a film festival. Authorities in Los Angeles consider him a convicted felon and a fugitive, and Switzerland says there has been an international warrant out on him since 2005.

Polanski's legal representatives are also appealing to Switzerland's federal criminal court to free the director. Galli said the Justice Ministry has submitted a letter to the tribunal explaining why it opposes release even on bail.

Legal experts say Polanski stands a minimal chance of a speedy release, even if his lawyers have suggested he be held under house arrest in his chalet in the luxury resort of Gstaad.

"In practice, I don't remember any case where a fugitive has been released on bail while awaiting extradition to a foreign country," said former Zurich prosecutor Peter Cosandey, adding that Polanski's ownership of an Alpine chalet doesn't aid his case greatly.

"He could easily disappear," Cosandey told The AP, referring to Switzerland's lax border controls. "He could just hop on a train to Germany. Coming by plane, you're often just waived on. By car, it's even easier."

Dieter Jann, another Zurich ex-prosecutor, has said extradition would be hard to fight, and he thought Switzerland had followed procedures correctly.

In Paris, Polanski's lawyers took note of the decision and said they would focus on convincing the court to free Polanski.

"In particular, Mr. Polanski undertakes to remain in Switzerland for the duration of the extradition procedure, and to respect all obligations that could be imposed on him to guarantee this commitment," said a statement.

Polanski was accused of plying the underage girl with champagne and part of a Quaalude pill during a modeling shoot in 1977, and raping her. He was initially indicted on six felony counts, including rape by use of drugs, child molesting and sodomy.

He pleaded guilty to the lesser charge of unlawful sexual intercourse. In exchange, the judge agreed to drop the remaining charges and sentence him to prison for a 90-day psychiatric evaluation.

However, he was released after 42 days by an evaluator who deemed him mentally sound and unlikely to offend again.

The judge responded by saying he was going to send Polanski back to jail for the remainder of the 90 days and that afterward he would ask Polanski to agree to a "voluntary deportation." Polanski then fled the country, on Feb. 1, 1978, the day he was scheduled to be sentenced to the additional time.

Galli confirmed that Washington has yet to file a formal request seeking extradition. But he said the U.S. probably wouldn't need its entire 60-day period to submit all documents.

"I assume this is a priority case in the United States," Galli said.

Polanski looks set to remain in prison for months as his case in the Swiss courts progresses. The criminal court has said it will rule on the filmmaker's request in the "next weeks," and a verdict in either direction can be appealed to the country's highest judicial body, the Federal Tribunal.

Galli said Polanski would remain in prison for the duration of this process.

Cosandey, an expert in international criminal cases, said Polanski's lawyers may seek to sway the court with promises such as a bail pledge as high as 1 million francs ($1 million).

"But it's hard to say if this will be successful," Cosandey said. "If the court just follows the formal treaty, he has to stay in prison. The fact that he's a prominent guy won't help him in Switzerland."

Polanski has received backing from directors and film stars in Hollywood and Europe, and from government officials in France and Poland, where he holds citizenship. But some of that support has waned since the original shock of his arrest, with leading French and Polish officials urging a more restrained reaction considering the crime.

In Switzerland, debate has raged among parliamentarians and cultural figures over the neutral country's role in arresting Polanski as he came to attend a government-backed festival. Few, however, have challenged the legality of his imprisonment and likely extradition.

Former Justice Minister Christoph Blocher said last week the director should have been warned — an assertion rejected by legal experts — but added that the case against Polanski now was quite simple and that he "must be extradited."

Polanski and the victim, Samantha Geimer, reached a $500,000 settlement in October 1993, according to documents recently released in Los Angeles.

Geimer, who long ago identified herself, sued Polanski in December 1988 when she was 25 years old, alleging sexual assault, intentional infliction of emotional distress and seduction. She has since joined in Polanski's bid for dismissal and has forgiven him.