Meeting privately with sex-abuse victims on the final day of his U.S. visit, Pope Francis apologized Sunday on behalf of the Catholic Church, saying he "deeply regretted that some bishops failed in their responsibility to protect children" and vowing that "everyone responsible will be held accountable."

Five adults - each of whom had been abused by priests, teachers, or family members - sat face to face with the 78-year-old pontiff at St. Charles Borromeo Seminary in Wynnewood, minutes before he delivered his strongest public remarks yet on an issue that has roiled the church worldwide.

"I have in my heart the stories of suffering and pain of the minors who were sexually abused by priests," the pontiff said, veering off script in an address to a room full of bishops and seminarians. "It continues to overwhelm me with shame that people who were charged with taking care of these tender ones violated that trust and caused them a profound pain."

He added: "God weeps."

It was a moment weighted with significance - both for the church in the United States, which has been plagued by sex-abuse scandals, and for Catholics in Philadelphia, where the archdiocese is still reckoning with its own troubled history.

During the half-hour 8 a.m. meeting, Francis listened to the stories of the three women and two men, prayed with them individually, and expressed his own "pain and shame" for their suffering, the Rev. Federico Lombardi, a Vatican spokesman, said.

"Words cannot fully express my sorrow for the abuse you suffered," Francis told them, according to remarks distributed later by the U.S. Conference of Catholic Bishops. "You are precious children of God, who should always expect our protection, our care, and our love."

In a nod to allegations that the church had ignored or covered up sex attacks on children, he added: "I am deeply sorry for the times when you or your family spoke out to report the abuse, but you were not heard or believed. Please know that the Holy Father believes you."

The meeting with victims was closed, however, and details were sparse, including whether any were from the Philadelphia region, which has been shattered twice in a decade by sweeping grand jury investigations of child-sex abuse by parish priests.

Archdiocesan officials did not respond to requests for information on the five participants. Lombardi declined to say how many were abused by priests or Catholic educators, but said at least two had been victimized by relatives. "We have to care for the health and safety of minors everywhere and in every milieu," he said.

Their conversation came days after Francis appeared to stumble in his first substantive comments on the issue during his U.S. tour. Victims' groups reacted angrily after, in a speech in Washington, the pope praised the "courage" of bishops for enduring and seeking reforms during the abuse scandal.

This time, Francis' words to the church leaders were more blunt. "I pledge to you that we will follow the path of truth wherever it may lead," he said. "Clergy and bishops will be held accountable when they abuse or fail to protect children."

Some critics called the decision to speak to a spectrum of victims a deliberate effort to sidestep the specific issue of clergy sex abuse - by cloaking it in a larger societal problem. Others dismissed the meeting as nothing more than a stunt.

"Is any child anywhere on Earth safer now that a pope, for maybe the seventh or eighth time or ninth time, has briefly chatted with abuse victims? No," said David Clohessy, director of the Survivors Network of Those Abused by Priests, the nation's most active advocacy group for clergy sex-abuse victims.

Those who observed Sunday's meeting at the seminary described it as powerful and very poignant.

"What we saw today before all of the bishops gathered here in Philadelphia was a very clear call - one of accountability," said Bishop Ed Burns of Juneau, Alaska, chairman of the U.S. Conference of Catholic Bishops' committee for the protection of young people. "You should have seen how moved he was - how truly moved he was - having that meeting."

Also attending were Philadelphia Archbishop Charles J. Chaput; Bishop Michael J. Fitzgerald, head of the Philadelphia Archdiocese Office for Child and Youth Protection; and Cardinal Sean Patrick O'Malley, the archbishop of Boston and chair of a clergy-abuse commission set up by the pope.

In his own speech Sunday before the pope's remarks, Chaput gave a nod to the emotional scars the scandals have left on the region.

"Our priests and our people were hurting from years of very painful news," he said. He also noted that many in the archdiocese hoped the pope's historic visit would serve as a salve.

Regardless of the optics, Catholics in town to attend the World Meeting of Families said they were glad to see Francis address an issue that has touched nearly every archdiocese in the nation.

"I think it's very important," said Kathy Philpott, 71, who traveled 26 hours by bus from Kansas City, Mo., to see Francis. "I think, for the health of the whole church, it needs to be emphasized, 'We're sorry it happened.' "

In Philadelphia, scathing grand jury reports in 2005 and 2011 exposed years of sexual predation by dozens of clergy, prompted suspensions of more than 30 priests, and led to the conviction in 2012 of the first senior church official in the United States criminally charged with protecting pedophile priests.

That supervisor - Msgr. William J. Lynn - was up until two months ago jailed at Curran-Fromhold Correctional Facility, where Francis greeted inmates later Sunday. Lynn has since been transferred to another prison while awaiting a ruling on his appeal.

A day earlier, Francis celebrated Mass with Cardinal Justin Rigali, the Philadelphia archbishop when Lynn was arrested and dozens of priests were suspended. Even the seminary itself, where Francis delivered his remarks to the bishops in slow and deliberate Spanish, had been the site of acts of alleged abuse detailed in both grand jury reports.

Francis' own record on the issue of clergy sex abuse has earned mixed reviews from victims and their advocates since his papacy began in 2013.

He has vowed to create a Vatican tribunal to prosecute bishops accused of failing to protect minors, and has accepted the resignations of three U.S. bishops accused of turning a blind eye to abusers ministering in their local parishes.

But in his off-the-cuff remarks Sunday, Francis adopted a penitent tone.

"Those who have survived have become true heralds of mercy. Humbly, we owe each of them our gratitude for their courage," he said, adding: "The crimes and sins of sexual abuse of minors cannot be kept in secret any longer."

And for some of the church's most critical abuse survivors, statements like that offered reason for hope.

"I was definitely encouraged," said State Rep. Mark Rozzi (D., Berks), who was elected largely on vows to stand as a voice for abuse victims in Harrisburg. "Now, it's time for [the bishops] to step up and embrace what he's saying. What they do from here will prove what they really believe."

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Jeremy Roebuck is an Inquirer staff writer. Regina Medina is a Daily News staff writer.

Inquirer staff writers Julia Terruso and Michael Boren contributed to this article.