Austrian authorities have charged a defrocked priest with sexually abusing 15 children as head of a Catholic boarding school.

They say Alfons August Mandorfer is also accused of torturing and neglecting young boys under his care between 1973 and 1993, when he was director of the school run by a monastery in the Upper Austrian town of Kremsmuenster.

But spokesman Andreas Pechatschek of the regional public prosecutor's office says most of the charges against the 79-year old are based on suspicion of "numerous crimes of a sexual nature."

Mandorfer was dismissed as a priest after several former pupils accused him several years ago of abuse.

Hundreds of alleged sexual victims of Catholic clergy in Austria have come forward in recent years as part of pedophilia accusations rocking the church internationally.