Authorities in Switzerland have decided not to extradite film director Roman Polanski to the US to face sentencing for a case dating back to 1977.

Polanski, 76, has been under house arrest in his Swiss chalet since December 2009 pending the decision.

He is wanted in the US over a conviction for unlawful sex with a 13-year-old girl.

Swiss Justice Minister Eveline Widmer-Schlumpf said the "restrictions on his liberty have been lifted."

A Swiss official said the US cannot appeal the decision.

Polanski faces arrest over his conviction for unlawful sex with an underage girl in 1977 should he ever return to the United States.

The director, who was originally charged with six offences including rape and sodomy, pleaded guilty to unlawful sex following a plea bargain.

But he left the US in 1978, before he could be sentenced, and has never returned.

He was taken into custody in Switzerland in September last year as he travelled from France to collect a lifetime achievement award at the Zurich Film Festival.

Polanski, whose films include Rosemary's Baby and The Pianist, was moved from prison and placed under house arrest at his chalet in the resort of Gstaad in early December.

'National interests'

The Swiss government declared Polanski a free man on Monday after rejecting the US extradition request.

The Swiss said US authorities failed to provide confidential testimony about Polanski's original sentencing procedure.

The Justice Ministry also said that national interests were taken into consideration in the decision.

A statement said: "The 76-year-old French-Polish film director Roman Polanski will not be extradited to the US.

"The freedom-restricting measures against him have been revoked."

It added: "The reason for the decision lies in the fact that it was not possible to exclude with the necessary certainty a fault in the US extraditionary request."