Former pope Benedict XVI failed to act over four child abuse cases when he was archbishop of Munich, a German probe into the Catholic Church has found.

Pope Benedict, then called Josef Ratzinger, held the position from 1977 to 1982. He has denied the accusations.

But a new report into historical abuse allegations carried out by a German law firm incriminated the former pope.

Abuse continued under his tenure, it is alleged, and the accused remained active in church roles.

The former pope, now aged 94, became the first Church leader to resign in more than 600 years in 2013. Since then, he has led a largely quiet life in the Vatican City.

The new report, commissioned by the Catholic Church, alleges he was told about the facts of child abuse cases while acting as archbishop, but took no action.

"Two of these cases concern abuses committed during his tenure and sanctioned by the state," lawyer Martin Pusch said as he announced the report.

"In both cases, the perpetrators remained active in pastoral care."