In many cases, pieces of evidence were destroyed or manipulated, it added.
Ackermann said in the statement that the aim of the study was to "gain more clarity and transparency about this dark side of our church, for the sake of those affected, but also to see for ourselves the wrongdoings and to ensure this can not be repeated".
If the state legislature approves, Kentucky will be the ninth US state to have an attorney general investigation into Catholic clerical sex abuse and the cover-ups by Church leaders.
According to research by experts from the Universities of Giessen, Heidelberg, and Mannheim, the actual number of victims was likely much higher, as researchers were not allowed access to the original church files.
The document, commissioned by the German Bishops' Conference, revealed that 1,670 clerics and priests had sexually abused 3,677 minors, mostly males, in the country between 1946 and 2014, Der Spiegel said.
Predatory clerics were often moved to new communities, where no warning was issued about their actions.
The German Bishops Conference said in a written response a few hours later that it regretted the leaking of the report, but that the study confirms "the extent of the sexual abuse" that took place. "We are dismayed and ashamed by it", said Bishop Stephan Ackermann on behalf of the conference.
The report deals another blow to the Church after clerical child abuse has been uncovered worldwide.
Only one in three (566 out of 1,670 accused) were subject to disciplinary hearings by the Church, and most got away with minimal punishment, said Die Zeit weekly, also citing the report. He said the Church had planned to provide counselling helplines for people affected by its contents.
The Catholic Church in Germany has acknowledged a "depressing and shameful" legacy of sexual abuse after a leaked study said clerics had abused thousands of children over a 70-year period.
The leaked study was published on the day Pope Francis summoned the presidents of the world's bishops' conferences to a summit on preventing clergy sex abuse and protecting children, responding to the greatest crisis of his papacy with the realisation that Vatican inaction on the growing scandal now threatens his legacy.
Earlier this week, the Vatican said it is preparing the "necessary clarifications" about accusations that top Vatican officials - including Pope Francis himself - covered up the sexual misconduct of the now-disgraced former cardinal Theodore McCarrick from the US.
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