Pope Benedict said on Saturday the Catholic Church could not accept gay marriage and urged young people to root out evil in society and shun a "lukewarm" faith that damages their Church.

The 84-year-old pope ended the third day in his homeland with a rally for more about 30,000 young people at a fairground outside the southern city of Freiburg, a Catholic area where he received the warmest welcome of his trip so far.

"The world in which we live, in spite of its technical progress, does not seem to be getting any better," he told the young people. "There is still war and terror, hunger and disease, bitter poverty and merciless oppression."

He urged them to root out all forms of evil in society and not to be "lukewarm Christians," saying that lack of commitment to faith did more damage to their Church than its sworn enemies.

Young people in the crowd cheered as he spoke.

"The Church is shown very negatively in the media these days so it is important for us young people to see we can also be proud of the Church, and the Church itself is not bad even if some people have let it down," said Kathrin Doerr, 26, who attended the youth rally.

Earlier, at a meeting with Orthodox Christian leaders, Benedict spoke out against abortion, euthanasia and gay marriage.

"We as Christians attach great importance to defending the integrity and the uniqueness of marriage between one man and one woman from any kind of misinterpretation," he said.

Communism's acid rain hurt faith

On the penultimate day of his trip, the pope straddled his homeland's religious and geographical divisions, praising the faithful for enduring communism's "acid rain" effect in former East Germany and then addressing cheering Catholic crowds in the west.

At a mass in the medieval main square during a subdued visit to the city of Erfurt, where only about seven percent of the people are Catholic, he praised eastern Germans who stayed loyal to the Church during oppressive years under Nazism and communism.

"You have had to endure first a brown and then a red dictatorship, which acted on the Christian faith like acid rain," he told the crowd from the altar, set against a hill dominated by Erfurt's cathedral and another Catholic church.

About two hours before the morning mass in Erfurt, a man fired an air gun at security staff at an Erfurt checkpoint in an apparent protest against the strict crowd-control measures, police said. The Vatican said the pope was never in any danger.

Benedict held a surprise meeting on Friday evening in Erfurt with victims of sexual abuse by priests. Church officials said on Saturday there were three men and two women present, chosen from many victims around Germany who had asked to meet the pope.

"The atmosphere of the meeting was rather relaxed," Vatican spokesman Federico Lombardi told a news conference. "It was very important that the Pope expressed he shares in the pain the victims suffered and that the Church will do everything to prevent that happening again in the future."

About 700 Germans have filed for compensation for abuse by priests and other Church personnel. A record 181,000 Germans left the Church last year, many in protest at the abuse scandal.