Germany's Roman Catholic Church said on Wednesday it had severed ties with criminologists commissioned to research sexual abuse by clergy in a row over the right to publish their findings.

The Church announced in July 2011 it would open its archives, which date back to the end of World War II, to shed light on abuse claims, tasking the northern Criminological Research Institute of Lower Saxony to analyse evidence.

But "mutual trust" between the Bishops' Conference and the head of the research centre has been "shattered", the bishops complained, adding they would now search for a new partner in the project.

Bishop Stephan Ackermann, appointed to handle issues surrounding claims of sexual abuse of minors, said they had been forced to terminate their contract with the institute "for an important reason with immediate effect".

"Trust is indispensable however for such an extensive and sensitive project," he said in the Bishops' Conference written statement.

But institute director Christian Pfeiffer told ZDF public television that church officials had wanted to approve their work before publication, which was "unacceptable".

Although cooperation in the initial months had been good, he said resistance started to appear in one diocese. "From there it was demanded that we bow to stricter wishes for control by the Church," he lamented.

"The contract (between us) had not foreseen such a thing," he added.

Since early 2010 and in common with other countries, Germany has been hit by revelations that hundreds of children were physically and sexually abused in institutions run by the Catholic Church.

Less than two years ago, the Church said it would open its complete archives from nine of its dioceses and release a cross-section of documents from the other 18 dioceses dating back to 2000 to researchers.

The row led Justice Minister Sabine Leutheusser-Schnarrenberger to weigh in.

"The accusation that censorship and desires for control hampered an independent accounting of the past should be quickly addressed once and for all by the chairman of the Bishops' Conference," she told Thursday's daily Sueddeutsche Zeitung.

Discussions will take place in the coming weeks to try to find a new partner in the research, the bishops said.

"The German Bishops' Conference is however still convinced of the need for a criminological investigation of sexual abuse of minors within the Church," the statement added.

Ackermann, who is bishop of the western city of Trier, contested the claims on public radio, saying they were only concerned about defining the original agreement and dealing with data protection and individual rights.

But Pfeiffer said former judges and prosecutors had been tasked with checking through the documents and the contract already ensured anonymity.

"Everything had been settled to the full from the point of view of data protection between the two sides," he said.