Pope Francis visits a prison in Philadelphia where he advises about 100 male and female inmates not to believe the "lie" that no one can change. Mana Rabiee reports.

On the final day of his visit to the United States, Pope Francis met with five victims of clergy sexual abuse at a Philadelphia seminary.

"God weeps," Francis told a gathering of bishops on Sunday (local time), departing from his prepared speech. "I commit to a careful oversight of the church to ensure that youth are protected, and I promise that all those responsible will be held accountable."

Pope Francis met later Sunday morning with about 100 inmates at the largest of Philadelphia's six prisons, telling them "all of us need to be cleansed, to be washed". He waded into the audience of prisoners in light blue uniforms, grasping their hands and touching their heads and hugging at least one.

Pope Francis tells bishops in Philadelphia that he had met with victims of clerical sexual abuse, adding that "God weeps" for them and that "all responsible will be held accountable".

The two meetings served as a reminder of a great tension within the Catholic church: Its handling of sexual abuse has been one of its most profound failings, but its message of redemption and forgiveness holds an enduring moral power.

"I am profoundly sorry that your innocence was violated by those who you trusted," Francis told the victims during the meeting at St. Charles Borromeo, according to his prepared remarks that were released by the Vatican.

"God weeps, for the sexual abuse of children cannot be maintained in secret, and I commit to a careful oversight to ensure that youth are protected and that all responsible will be held accountable," Francis said in Spanish while in the City of Brotherly Love for a big festival on the Catholic family.

The spokesman for Pope Francis says the Philadelphia meeting with abuse advisors was not only with victims of clergy abuse, and says the Pope wants to address the problem of abuse in context of families.

"We promise to support your continued healing and to always be vigilant to protect the children of today and tomorrow."

It was Francis' second such meeting: He received sexual abuse victims at the Vatican in July 2014.

But in an apparent effort by the church to reshape the discussion, the Vatican said not all five of the victims on Sunday were abused by members of the clergy; some of the three women and two men had been victimised by relatives or educators.

MARK MAKELA / REUTERS Pope Francis leads a mass at the Cathedral Basilica of Saints Peter and Paul in Philadelphia.

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He was accompanied by Cardinal Sean Patrick O'Malley of Boston, and Philadelphia Archbishop Charles J. Chaput. They met with three women and two men who were abused as minors.

The Vatican had repeatedly refused to say whether the pope would meet with abuse victims, describing such a meeting as a personal encounter, not a media event. Victims and their advocates have criticised the pope for paying too little attention to the sexual abuse crisis that shocked Philadelphia and much of the nation, and that left the US Catholic Church with deep scars.

OSSERVATORE ROMANO/REUTERS Pope Francis pauses to pray at the 9/11 Memorial plaza in New York.

Kevin Waldrip, 64, who was abused on his 13th birthday by "a priest who was one of the first to be convicted," was unmoved by the pope's meeting and by his statement afterwards.

"God may weep," he said, "but [the pope] certainly doesn't and the church doesn't. They've proven it again and again."

The pope's meeting with sexual abuse victims came hours before he is scheduled to celebrate an outdoor Mass before a crowd that could swell into the hundreds of thousands.

The afternoon Mass is the climax of a historic six-day journey to Washington, New York and Philadelphia that has riveted Americans' attention, giving Francis a broad audience for his messages about serving the poor, bolstering families, caring for the environment and welcoming newcomers to the country.

If Francis's message to abuse victims was that the church can and will change, then his message to prisoners was that they can find redemption.

Inmates at the Curran-Fromhold Correctional Facility include some who are awaiting trial and others who have been convicted of crimes ranging from selling drugs to rape and murder.

"This time in your life can only have one purpose: to give you a hand in getting back on the right road, to give you a hand to help you rejoin society," Francis told them, speaking before a stately walnut chair that inmates built for him.

He spoke of Jesus washing the feet of his disciples at the Last Supper, and said that everyone - including prisoners, including the pope himself - has something "we need to be cleansed of, or purified from."

"Life is a journey, along different roads, different paths, which leave their mark on us," he said.

Reaching out to prisoners and other members of society's most marginalised - and in some cases, despised - is a hallmark of Pope Francis's. Shortly after he was elected as pontiff, he washed the feet of inmates at a juvenile detention centre in Rome. He did so again in April.

Marliene McCarthy, 76, a Sister of Mercy, huddled with a small crowd of devotees on a street corner near the prison, hoping for a glimpse of the pontiff. She said the pope's prison visit encapsulates his broad view of life as not just about abortion but on the conditions of the poor during their lives.

"This location is him. It's the poor, people of colour who end up in prisons. If you have some advantage you don't land there," McCarthy said.

Francis's earlier address before the bishops on Sunday morning returned to some of his favourite themes, criticising what he described as society's obsession with material goods.

"Today consumerism determines what is important. Consuming relationships, consuming friendships, consuming religions, consuming, consuming... Whatever the cost or consequences," Francis said in his prepared remarks.

But it was his unscripted comments about child sexual abuse, delivered at the beginning of his address, that came as something of a surprise and won the greatest notice. "It continues to be on my mind that people who had the responsibility to take care of these tender ones violated that trust and caused them great pain," he said.

Some bishops in the audience praised the pope's statement as forthright and necessary. But not everyone was satisfied.

Robert Hoatson, a former priest who has become an advocate for sexual abuse victims, felt the pope's comments brushed too quickly over the serious issue. "It's going to cause more distress, more traumatization, re-abuse," he said, "because it seemed like a side note."

Earlier in the week, the pope had praised the "courage and "pain" of US bishops in dealing with the scandal, drawing sharp disapproval from victims' advocates who criticised him for failing to extend the same sympathy to survivors of sexual abuse by clergy.

Phil DiWilliams, who as a high school freshman was sexually assaulted by a priest, questioned whether the pope's remarks would translate into action.

"They'll be held accountable, meaning what?" he asked. "They don't go to jail, very few go to jail. The guy who molested me is in a home, supposedly doing prayer and penance."

Ever since his airplane touched down in Washington last week, this pope has waded into some of the country's most charged cultural wars, urging Americans to honour their country's history by embracing immigrants and respecting religious freedom.

He has addressed some of the nation's most powerful people, including at the White House and on Capitol Hill. But many of the moments that seemed to resonate most deeply, with Catholics and non-Catholics alike, have been his intimate interactions with the disadvantaged, the disabled and the young.

In Washington, he turned down an invitation to dine with members of Congress, choosing instead to break bread with hundreds of homeless men and women. In New York, he told schoolchildren in East Harlem, many of whom were Hispanic, that immigrants make a society stronger.

And shortly after arriving at the Philadelphia airport, he climbed out of his black Fiat to bless a young boy with cerebral palsy.

The boy's mother said she could not understand Francis's words, which were not in English. But she understood the emotion: "Love."

"Viva, Papa!" jubilant crowds have shouted everywhere the Argentine pope has gone. "Pray for me" has been his frequent refrain.

"He really cares for us," said Monserrat Valencia, 46, a Mexican immigrant from a small town in Pennsylvania, after listening to the pontiff speak at Independence Hall on Saturday. "The rights to all kinds of equality, spiritual and material - he said everyone deserves that."

Sunday's Mass is part of the World Meeting of Families, a global gathering of Catholics that happens every three years and was hosted this year by the City of Brotherly Love. The pope first addressed the group on Saturday night, when - departing almost entirely from his prepared remarks - he gave a heartfelt, animated speech in Spanish about the importance and joys of family, even throwing in a couple of jokes about mothers-in-law and marriage.