Pope Benedict XVI said he is "deeply sorry" for pain, suffering caused to victims of clergy sex abuse.
The pope said he wanted to acknowledge the "shame that we have all felt as result of the sexual abuse of minors by some clergy" in Australia.
He said the deeds of clergy responsible for abuse were a grave betrayal of trust that had caused great pain, had damaged the Roman Catholic church, and deserved unequivocal condemnation.
The pope spoke at a Mass Saturday attended by Australia's Roman Catholic bishops and seminarians.
Support groups for victims of church abuse in Australia, whose numbers were not known, have demanded the pope make a full and open apology for clergy abuse and do more to prevent future abuse.
Plea for unity against violence
His statements followed his earlier plea for all faiths to unite against violence.
He told representatives of Islam and other faiths that they must unite to combat religion's role in "sinister and indiscriminate" violence.
Without mentioning terrorism directly, the pontiff said there were those in who were using religion "as a cause of division rather than a force for unity" in a 40-minute exchange with Australian Jewish, Muslim, Hindu and Buddhist leaders in Sydney.
"In a world threatened by sinister and indiscriminate forms of violence, the unified voice of religious people urges nations and communities to resolve conflicts through peaceful means and with full regard for human dignity," Benedict told the leaders, gathered in the gothic surrounds of Australia's largest Roman Catholic cathedral as part of the church's global youth festival.
Harmony between religion and public life is especially important in these days, he said.
The remarks come as the Vatican tries to cool lingering anger among Muslims over a speech Benedict gave in 2006 that appeared to associate Islam with violence. Benedict quickly apologized for the link.
In reply, the delegates from the other creeds welcomed the pope's inclusionary stance, though Sheikh Mohamadu Saleem of the National Imams Council of Australia noted discrimination between faiths was still a problem.
Muslims should be more understanding of other religions, he said, adding: "At the same time, a significant amount of the Christian groups and other religions must overcome their prejudice to Muslims and Islam."
Church in 'crisis'
The meeting was one element of a busy Friday schedule for the 81-year-old pontiff at World Youth Day, which organizers say has attracted more than 200,000 young Catholics to Australia's largest city. Two days into his four-day official program, the pope looked fit and energetic.
Benedict, who last week said his church was in "crisis" in the West because of many had lost faith in God, held a separate meeting with deputies of Christian denominations.
He urged them to cooperate against secularism and apathy — saying those shared problems were greater than any differences among them.
"I think you would agree that the ecumenical movement has reached a critical juncture," he told the Christian representatives. "We must guard against any temptation to view doctrine as divisive and hence an impediment to the seemingly more pressing and immediate task of improving the world in which we live."
The pope blessed the opening scene of a live reenactment of the stations of the cross — the Bible's depiction of Christ's last days — that was played out through Sydney, with some of the city's most recognizable landmarks in the backdrop.
Pilgrims lined the streets to watch the recreation, which stretched over three hours and included often stark scenes of brutality toward Jesus, including his being nailed to a cross. As night fell on a clear but cold midwinter day, many watching clutched each other and wept openly. Organizers estimated the live television audience for one of the festival's most dramatic events topped 500 million.
'Cult of material possessions'
Benedict met later with a group of disadvantaged youth at a Catholic university campus, where he decried "the cult of material possessions."
"Our materialistic society," he said, too often sought happiness "by acquiring as many possessions and luxuries as we can."
On Saturday, the pope will spend part of the day with bishops and other Catholic officials, and has signaled he may make express regret about past sexual abuse by Australian clergy as he did during his trip to the United States earlier this year.
Later, he will for a couple of hours join a mass of pilgrims camping out at a horse racetrack in Sydney — the only open space so close to town that could accommodate the size of the crowd — at an overnight vigil. He will return there by helicopter Sunday to hold Mass, the culmination of the festival.
A small group of protesters, who have criticized the church's handling of the abuse scandal that has dogged it in recent years, gathered Friday near St. Mary's Cathedral, where the pontiff is staying. The waved placards reading "Hands off our kids" and "Clergy sexual abuse turns Christianity upside down." The demonstration ended without incident.