The quiet 11th-century Neresheim Abbey in southern Germany has swept into the spotlight after the discovery of "unaccounted-for millions" in its possession, raising questions about its origin.

Father Albert Knebel revealed that he had discovered a "fortune" amounting to $5 million in the estate left by the late Abbot Norbert Stoffels, Britain's Independent newspaper reported.

Stoffels was Nereseheim's "guiding spiritual light" from 1977 until his death in 2012.

Knebel admitted that the money was neither registered on the abbey's accounts or to anyone in the administration. Abbey staff also know nothing about its existence.

The money is a mystery as no one can explain if it was a money-laundering operation and what it may have helped to finance.

"Our foremost concern is to find out where this money comes from," Knebel said in a statement.

State prosecutors in northern Germany say they have opened an investigation expressing suspicion that the cash may have come from a money laundering operation.

A spokesman for the prosecutor's office said the case faced legal complications because the prosecutors were involved in a dispute with a lawyer who had laid claim to part of the "unaccounted-for millions."

Neresheim Abbey said that the lawyer tried to claim part of the money through the courts.

"So far he has been unable to provide legally binding documents which could justify his claims," explained Knebel.

He stressed that he and his fellow monks are not interested in the money as it was never included in the abbey's finances.

The money scandal that hit Neresheim Abbey is a new twist for Germany's Catholic Church.

Early this year, Franz-Peter Tebartz-van Elst, the so-called "Bishop of Bling," was forced to resign after spending $47 million to renovate his official residence.

Christian Weisner, spokesperson for the "We Are Church," said the German Catholic Church needs deal seriously with the controversies it is facing, or it will continue to find its 23 million followers diminishing.