The leader of Germany's Jewish community, Paul Spiegel, said Friday he was "extremely impressed" by Pope Benedict XVI's speech during a landmark visit to Cologne's synagogue.

"I was extremely impressed by what he said and how he said it. He condemned the crimes of the Nazis without any ifs and buts," Spiegel told Germany's ARD television.

During only the second visit to a synagogue by a pope in the modern history of the Catholic Church, the pope described the extermination of six million Jews by the Nazis as an "unimaginable crime."

Spiegel, the president of the Central Council of Jews in Germany, said at a news conference later that he welcomed the pope's call for Jews and Christians to work more closely together to overcome their sometimes fractious relationship.

He added he was "particularly impressed that he said the roots of Christianity lie in Judaism."

Benedict XVI, who served briefly in the Hitler Youth during the war when membership of the Nazi organization was compulsory, paused to pray at a memorial to the six million Jews killed in the Holocaust as he began the landmark visit.

Speaking in the synagogue which was destroyed in the anti-Jewish Kristallnacht attacks in 1938 and rebuilt in 1959, he called the Holocaust "this unspeakable and previously unimaginable crime."

Pope warns of new threats

"In the 20th century, in the darkest period of German and European history, an insane racist ideology, born of neo-paganism, gave rise to the attempt, planned and systematically carried out by the regime, to exterminate European Jewry," he said.

The pope warned that new threats of racism and anti-Semitism were always lurking. "It is a particularly important task, since today, sadly, we are witnessing the rise of new signs of anti-Semitism and various forms of a general hostility towards foreigners," he said.

"How can we fail to see in this a reason for concern and vigilance? The Catholic Church is committed -- I reaffirm this again today -- to tolerance, respect, friendship and peace between all peoples, cultures and religions," he said.

In his speech to Jewish leaders, Benedict also referred to John Paul II, saying that "in considering the Jewish roots of Christianity, my venerable predecessor, quoting a statement by the German bishops, affirmed that 'whoever meets Jesus Christ meets Judaism'."

Jewish leader calls on Holocaust files to be opened

During the pope's visit, a leader of Germany's Jewish community called on the pope to fully open the Vatican's archives on the Holocaust.

In a speech welcoming the 78-year-old German-born pope, Abraham Lehrer called on the pope to "fully open" the archives, reminding him that as the former head of the Vatican Congregation for the Doctrine of the Faith, he had helped release some of the documents they contained for public scrutiny in 1998.

Lehrer said he would welcome such a move as a "further sign" of the Vatican's goodwill towards the Jewish community and allow both sides to continue "peaceful and critical" examination of the history of their troubled relations.

"As leader of the Catholic Church, you have a special responsibility. Your actions serve as a model for the Church," Lehrer told the pope.

The archives contain diplomatic correspondence and Church documents which could throw light on the degree of Vatican knowledge of Nazi efforts to deport and exterminate Europe's Jews.

Jewish groups have strongly opposed plans set in motion by Benedict's predecessor John Paul II to elevate wartime pope Pius XII (photo) to sainthood, claiming he did little or nothing to prevent Jews being deported.

Lehrer praised Benedict XVI, who succeeded John Paul II in April, as a "builder of bridges between religions," adding that his visit was "an extraordinary event of great political and religious significance."

The head of the German Bishops' Conference, Cardinal Karl Lehmann, acknowledged at a news conference later that part of the archives was already open "but we must continue to work to open the archives of the Pius XII period."

The visit to the synagogue was the highlight of the second day of the 78-year-old pope's four-day visit to Germany, the first foreign trip of his pontificate.

Discussions with Köhler behind closed doors

Earlier in the day the pope met with German President Horst Köhler, adding a political touch to a day dominated by the highly symbolic visit to the synagogue and talks with Protestants.

After his jubilant reception Thursday, when around 400,000 young Catholics welcomed him back to his native country, Benedict's agenda on the second day of his visit began with closed-door talks at the presidential villa in nearby Bonn before moving on to the religious meetings in Cologne.

Benedict waved to a small crowd outside the Villa Hammerschmidt, the presidential residence in the former German capital, and shook hands with children after the meeting.

"This World Youth Day shows that Catholics are not a minority but come from all around the world," Köhler told journalists before the Pope arrived. "It is good and it will do good for Protestants as well," said Köhler, a Protestant.

About half of the Christians in Germany, home of Martin Luther's Reformation, are Protestant.