Swedish police have freed a 14-year-old girl who was allegedly trafficked to Sweden from Belgrade and held as a sex-slave for a year by a mentally-deranged man, media reports said Wednesday.

Police refused to comment on the reports, except to confirm that there is a case under investigation.

The Daily Expressen described the girl's captor as a 25-year-old mentally handicapped man.

His family believed he would get better if he had a wife, so they bought the girl for him from her father in the Serbian capital, paying 1,000 euros ($1,360), the paper said.

Her ordeal began in September 2010.

"The girl was forced to get engaged in line with Roma customs with the 25-year-old, and was taken to the family's apartment ... where she was locked up," Expressen reported.

The girl, whose name was not disclosed, has told police she was subjected daily to threats, physical abuse and rape during her captivity in Sweden's second city Gothenburg, the paper said.

A Gothenburg court has detained four people in the case on suspicion of human trafficking, including the girl's captor and her father, Swedish news agency TT said.

Her captor and a 40-year-old woman are also suspected of rape.

Expressen said the girl became pregnant and suffered a miscarriage at one point during her ordeal.

"She is very, very happy to be free of this hell. In videotaped police interrogations she has talked extensively about what she has gone through," an unidentified source told Expressen.

It was not immediately known how the case came to the police's attention.

Expressen said police freed the girl in late October or early November in a raid on the apartment.

According to TT, the case is being handled by prosecutors in the international prosecution unit.