A German Jewish leader touched a sore spot in relations with Catholics on Friday when he urged Pope Benedict to open up all the Vatican's archives dealing with World War Two and the Holocaust.

Welcoming him on a historic visit to a synagogue in Cologne, Abraham Lehrer told the German-born pontiff he had a special responsibility to open files that critics say would show how much Pope Pius XII knew about the Nazi slaughter of Jews.

Jewish groups accuse Pius of turning a deaf ear to the Holocaust. The Vatican says he worked behind the scenes to save them and refrained from condemning the Nazis openly for fear of sparking reprisals across Europe.

The Vatican has opened its diplomatic archives up until 1939 the year that Pius was elected, but does not plan to unseal its wartime records until at least 2009.

"For us, a complete opening of the Vatican archives covering the period of World War Two, sixty years after the end of the Shoah (Holocaust), would be a further sign of historical conscience and would also satisfy critics," Lehrer said.

"You grew up in Germany during a terrible time," he told Benedict during the first papal visit to a synagogue in Germany. "We not only see in you the head of the Catholic Church but also a German who is aware of his historical responsibility."

Benedict did not answer Lehrer's plea, but his pre-written address included a reference to the need to reach "a mutually accepted interpretation of still disputed historical issues".

The synagogue the Pope visited was destroyed in the Nazis' anti-Jewish Kristallnacht riots in 1938 and rebuilt in 1959.

Earlier efforts collapse

The wartime role of Pius, branded "Hitler's Pope" by his critics, has been one of the thorniest issues facing Catholics and Jews since they began a process of reconciliation in 1965.

The Vatican and Jewish groups set up a mixed Catholic-Jewish historians' commission in 1999 to study the Vatican archives in the hope of settling the dispute. It collapsed the following year because the Vatican would not allow full access to files.

Lerner noted that Benedict, while he was still Cardinal Joseph Ratzinger, opened up the archives of his Congregation for the Doctrine of the Faith (CDF) in 1998.

These files uncovered a wealth of information about the Inquisition, which was the CDF's original name and purpose, and the Church's centuries-long Index on Prohibited Books.

Historians say the Church archives opened so far show the Vatican was receiving detailed accounts of Nazi anti-Semitic acts only weeks after Adolf Hitler came to power in 1933.

But only letters to the Vatican and cables from Vatican embassies in Berlin and Munich were released. Holocaust information from other sources, such as cables from Vatican diplomats in France or Poland, have not been released.

Hoping to prove Pius was not anti-Semitic or pro-German, the Vatican opened its Germany archive for 1922-1939 two years ago. But the 640 files provided fuel for both critics and supporters.

One of the most evocative documents was a plea for a papal intervention against the Nazis in 1933 by Edith Stein, a Jewish convert to Catholicism who later died in a concentration camp.

Stein wrote to Pius XI, Pius XII's predecessor, that the Vatican could not keep silent about Nazi anti-Semitism:

"All of us, who see the actual situation in Germany...fear the worst for the image of the Church worldwide if this silence is prolonged further.