A renowned German Catholic boys' choir led for three decades by the brother of Pope Benedict XVI on Friday admitted sex abuse allegations as the Church struggles to contain a spreading scandal.

The famed Domspatzen (Cathedral Sparrows) choir in the southern city of Regensburg, founded in 975, acknowledged in a "letter to parents" published on its website that a child had been abused in the 1950s.

"To our knowledge the boarding school principal at the time was tried and convicted. He has since died," the choir said.

It also said a former choir member in the early 1960s had recently told a newspaper that he had been sexually molested. An ombudswoman from the local bishopric, Birgit Boehm, has attempted to contact the man.

"At this point it is not clear whether the alleged abuse occurred in our institution or the Etterzhausen preschool," it said.

"The Foundation Regensburg Domspatzen has to date no other evidence of sexual abuse" but pledged to follow up on any further accusations.

"For this reason we ask all who have learned of sexual abuse of minors in our institution by clerics or other church staff, or are victims themselves, to report to a member of the board" or Boehm.

However a spokesman for the Regensburg bishopric, Clemens Neck, told AFP that it had further "information about alleged abuse between 1958 and 1973".

"We plan to investigate with total transparency," he said.

The pope's brother, 86-year-old Georg Ratzinger, led the Domspatzen between 1964 and 1993. He has not been accused of abuse.

The latest revelations come days after the German Episcopal Conference put Stephan Ackermann, bishop of the western city of Trier, in charge of probing sexual exploitation of children at a number of Catholic institutions in the country.

The chairman of the Conference, Robert Zollitsch, is to meet with the pope March 12 at the Vatican to discuss the cases.

The scandal in Germany broke in January when an elite Jesuit school in Berlin admitted the systematic sexual abuse of its pupils by two Roman Catholic priests in the 1970s and 1980s.

Last month two priests and a college rector resigned over abuse cases.

An independent investigator hired by the Jesuit order said that so far around 120 people had come forward alleging abuse.