Ansbach, Germany - A 63-year-old doctor charged with misusing his power to sexually abuse his patients apologized on Monday on the opening day of his trial in Germany's southern state of Bavaria.

"They were my intimate friends and now they have become victims," the physician told the court in Ansbach. He has not been identified under Germany's strict privacy laws.

The prosecution said the doctor exploited the trust of three mentally unstable patients to have sex with them, sometimes without treating the women. One of the women was allegedly raped.

The defendant admitted to having sex with the women but was unable to say how many times.

The doctor's indictment charges his involvement in 122 cases of patient sexual abuse between 2012 and 2015.

A trained psychotherapist, the doctor committed the acts either in his practice or in the women's homes, the prosecution said. He faces up to five years in prison.

The doctor regularly asked mentally ill patients to come to his surgery - usually in the late evening hours, prosecutors said.

He is alleged to have told the women that sex was part of the therapy. Eventually, one of the women called the police.

The accused admitted the allegations in a statement made through his lawyer in February.