Munich  - A smooth-talking Swiss gigolo who allegedly preyed on wealthy women goes on trial on Monday charged with extorting millions of dollars.

Amongst the alleged victims is BMW car heiress Susanne Klatten, 46. The publicity-shy mother-of-three is reputedly Germany's richest woman, with a large stake in luxury carmaker as well as a pharmaceuticals company.

Helg Sgarbi, 44, is accused of trying to extort 14 million euros (17.5 million dollars) from Klatten after he threatened to publicise secret video recordings of them having sex.

It is unclear whether Klatten and three other women Sgarbi is alleged to have seduced and defrauded will testify against him.

Sgarbi, who has been in custody since his arrest in Vomp, Austria last year, faces four counts of serious fraud and two charges of attempted blackmail.

Anton Winkler, the prosecutor, said, "If the accused does not admit the charges in their entirety, the victims have to testify."

Media claim Sgarbi was a serial seducer who approached his wealthy victims at luxury hotels and duped them into thinking he loved them.

He persuaded them to give him millions of euros by inventing stories about needing money to pay compensation for a child he injured in a car accident.

In some versions the accident happened in the United States, in others it was in Italy where the Mafia got involved and was demanding "silence" money from him.

Two of the women handed over hundreds of thousands of euros. Klatten was also tricked parting with 7 million euros. But Sgarbi wanted more.

Klatten went to police and exposed Sgarbi after he contacted her asking for a large sum of money in return for his silence.

"That was a moment of clarity: you are now the victim and you have to defend yourself. I am now defending myself in the name of all women in my family and also in the name of many other women," Klatten told the newspaper Financial Times Deutschland in her only interview on the subject.

News reports have portrayed Klatten as a dutiful businesswoman willing to endure public shame to bring Sgarbi to justice.

Sgarbi is alleged to have handed over part of the money to Ernano Barretta, an Italian who was released last month from pre-trial custody in Italy on the grounds there was not enough evidence against him.

The trial is expected to last until early April. German law punishes serious fraud with up to 10 years' prison and blackmail with up to 15 years. dpa