Vatican City (AFP) - Pope Francis announced Monday that the Vatican will open the secret archives of Pius XII in March next year, which could shed light on his actions during World War II.

Researchers have long sought to examine the archives to discover why Pius XII (1939-1958) did not intervene more against the Holocaust perpetrated by the German Nazis, an attitude denounced by Jewish groups as a form of passive complicity.

"I have decided that the opening of the Vatican Archives for the Pontificate of Pius XII will take place on 2 March 2020," the pope said. The date is the 81st anniversary of the election of Eugenio Pacelli to the papacy.

"The Church is not afraid of history," added Francis, recalling that Pius XII found himself as head of the Roman Catholic Church "at one of the saddest and darkest moments of the 20th century".

Francis said he made the decision confident that serious historical research would evaluate "in the proper light and with appropriate criticism, the praiseworthy moments of the Pontiff and, without any doubt, also moments of serious difficulties, of tormented decisions...".

For many historians, pope Pius XII could have condemned more forcefully the massacre of Jews by the Nazis, but failed to do so out of diplomatic caution and to avoid putting Catholics in danger in occupied Europe.