In an interview published Friday in the Spanish newspaper La Vanguardia, Francis condemned anti-Semitism, saying it was a "continuing" problem that was more prevalent in right-wing parties in Europe, and called Holocaust denial "madness."
He also repeated that he did not rule out resigning as pope like his predecessor Benedict XVI if he felt he could no longer rule the 1.2 billion-member Roman Catholic Church, saying that he would ask God for guidance "when the time comes."
In his most comprehensive remarks to date on the controversy surrounding Pius, Francis confirmed that he intended to open up the Vatican archives for the wartime period but he did not say when that would happen.
"They will shed a lot of light," he said.
Some Jews have accused Pius, who ruled from 1939 to 1958, of turning a blind eye to the Holocaust. The controversy has put a strain on Catholic-Jewish relations for decades.
The Vatican says Pius worked behind the scenes to save thousands of Jews and did not speak out more forcefully for fear that his words could have led to more deaths of both Jews and Christians at the hands of the Nazis.
"I don't want to say that Pius XII did not make any mistakes - I myself make many - but he has to be seen in the context of that era. For example, was it better for him not to speak out so that more Jews were not killed, or that he speak out?" he said.
Francis, the first non-European pope in 1,300 years, said that during the war his predecessor was seen as "a great defender of Jews", and that his critics "have dumped all kinds of things on poor Pius XII."
He said Pius ordered the Church to hide many Jews in the convents of Rome and other Italian cities, that he sheltered Jews in the papal summer residence south of Rome and that 42 children of Jews and other refugees were born in his apartments there.
He said he sometimes "breaks out in an existential rash" when "everyone takes it out against the Church and Pius XII" and "forgets" the responsibility of the great wartime powers.
"Did you know that they knew perfectly the train network the Nazis used to take the Jews to concentration camps? They had photos. But they didn't bomb the train tracks. Why? It would be good if we could talk a little about everything," he said.
Last month, Francis visited the Yad Vashem memorial to Holocaust victims in Jerusalem. The Yad Vashem's website, addressing the issue of the allies' activity during the war, says: "In practice, no military initiatives were taken to prevent or delay the extermination."
Jewish groups have asked Francis and his predecessors to freeze the process that could lead to sainthood for Pius until the all the World War Two era archives are opened to historians, saying Catholic-Jewish relations could be harmed if the process moved ahead.
Speaking to reporters on the plane returning from Jerusalem last month, Francis said the sainthood cause for Pius was stalled because he had not been credited with performing a miracle, which Church rules require, suggesting it was not stalled because of any outside pressure.