Pope Benedict has warned German lawmakers not to abuse power, referring to excesses in Adolf Hitler's Nazi Germany as a lesson in history.

In a speech to the German parliament Thursday, at the start of his first state visit to his native country, the pope said Germans know from experience what happens when power is corrupted. He described Nazis as a “highly organized band of robbers capable of threatening the whole world and driving it to the end of abyss.”

Pope Benedict, who is German, also praised Nazi resistance movements for sticking to their beliefs at great risk. He said those movements did a “great service to justice and to humanity as a whole.”

The pope spoke amid protests outside the Reichstag parliament building in Berlin, and a boycott by about 100 lawmakers from opposition parties.

Earlier Thursday, at a formal welcoming ceremony at President Christian Wullf's Bellevue palace, the pontiff warned Germans of the danger of ignoring religion. He also acknowledged the damage caused by the sex abuse scandal that has rocked the Roman Catholic Church.

German Chancellor Angela Merkel and President Wullf greeted the Bavarian-born pontiff upon his arrival at Berlin's Tegel airport at the start of his four-day visit. A few protestors carrying banners about sexism, homophobia and anti-Semitism gathered outside the airport.

In a meeting, the pope and Chancellor Merkel discussed the euro crisis and turmoil on the financial markets.

As many as 20,000 people were expected to demonstrate outside of parliament. Those expected at the demonstration include gay and lesbian rights organizations and groups that want to see reform in the church — on issues including divorce, ordination of women priests, abolishing celibacy for clergy, and support for victims of sexual abuse by priests.

Tens of thousands of Catholic faithful were expected to attend an open-air Mass at Berlin's Olympic Stadium Thursday night. During his visit, the 84-year-old pontiff will also hold Mass in the cities of Erfurt and Freiburg.

Germany's 50 million Christians are almost evenly divided between Protestants and Catholics, and many see the pope's visit as a chance to promote greater understanding between the two churches.