The wartime letter was rediscovered by an in-house Vatican archivist.Newly unearthed wartime correspondence from Pope Pius XII indicates he may have known about the Holocaust earlier than previously believed.
Italian newspaper, Corriere della Sera, on Sunday reproduced a typewritten letter that was recently found in the Vatican archives.
The letter, dated Dec. 14, 1942, appears to conflict with the Holy See's official position at the time, which was that the information it had was vague and unverified.
Written by Father Lother Koenig, a Jesuit who was in the anti-Nazi resistance in Germany, the letter was addressed to the pope's personal secretary at the Vatican, Father Robert Leiber, also a German.
The letter was rediscovered by an in-house Vatican archivist and made public with the encouragement of Holy See officials.
Vatican archivist Giovanni Coco told the Corriere that the importance of the letter was "enormous, a unique case" because it showed the Vatican had information that labor camps were actually death factories.
In the letter, Koenig tells Leiber that sources had confirmed that some 6,000 Poles and Jews a day were being killed in “SS-furnaces” at the Belzec camp near Rava-Ruska, which was then part of German-occupied Poland.
Asked by the Corriere interviewer if the letter showed that Pius knew, Coco said: "Yes, and not only from then."
The letter made reference to two other Nazi camps - Auschwitz and Dachau - and suggested that there were other missives between Koenig and Leiber that either have gone missing or have not yet been found.
Supporters of Pius say he worked behind the scenes to help Jews and did not speak out in order to prevent worsening the situation for Catholics in Nazi-occupied Europe. His detractors say he lacked the courage to speak out on information he had despite pleas from Allied powers fighting Germany.
The letter's discovery comes more than four years after Pope Francis decided to open up the Vatican archives on Pope Pius XII, whom many Jewish groups have accused of doing little to stop the Holocaust.
Francis declared that the church "isn't afraid of history," and said the Vatican Secret Archives would be open to researchers.
"The church isn't afraid of history. On the contrary, it loves it, and would like to love it even more, like it loves God," Francis told the staff at the archive. "Thus, with the same trust of my predecessors, I open, and entrust to researchers, this patrimony of documentation."
Reuters contributed to this report.