PHILADELPHIA - Pope Francis met with sex abuse survivors, bishops and prison inmates Sunday morning, the start of his final day in the United States.

Francis began the day by meeting with five adult victims of child-molesting priests.

Later, in remarks to bishops at the St. Charles Borromeo Seminary in Philadelphia, he lamented the sexual abuse of children by Roman Catholic clergy and vowed to protect those affected.

Francis deviated from prepared remarks at that meeting with about 300 Catholic bishops and said God weeps at such abuses.

"I hold the stories and the suffering . . . of children who were sexually abused by priests, deep in my heart," Francis said in Spanish. "I remain overwhelmed with shame that men entrusted with the tender care of children violated these little ones and caused grievous harm. I am profoundly sorry."

The pope promised to make sure the issue stays in the open.

"The crimes and sins of the sexual abuse of children must no longer be held in secret," he said. "I pledge the zealous vigilance of the church to protect children and the promise of accountability for all."

He committed to work "to protect those minors."

After the meeting concluded, Francis was flown by helicopter to Curran-Fromhold Correctional Facility in Philadelphia.

He arrived at the facility and began speaking with inmates just after 10:30 a.m. He talked with them inmates about the difficult times in their lives they face while incarcerated, and said "all us need to be cleansed, to be washed."

He repeated the metaphor of Jesus' washing his disciples feet when they came to see him, even though some refused.

"We know in faith that Jesus seeks us out," Francis said in remarks that were translated from Spanish to English. "He wants to dress our wounds . . . he doesn't ask where we have been, he doesn't question us about what we have done."

After speaking, he greeted and shook the hands of about 100 prisoners in powder blue jumpsuits as well as some of their family members and correction officers who were there to watch the pontiff speak. Inmates presented Francis with an altar chair that they made for him at the jail.

Earlier in the morning, the Vatican press office said the pope met with five victims of clergy sex abuse for about 30 minutes earlier Sunday and prayed with them at seminary, accompanied by Cardinal Sean O'Malley of Boston, Archbishop Charles Chaput of Philadelphia and Auxiliary Bishop Michael Fitzgerald of Philadelphia, according to a U.S.-based Vatican spokesman.

The unexpected statement represented the first time Francis addressed head-on the issue from the victim's perspective during his historic visit to the United States that began Wednesday in Washington D.C.

"Sexual abuse cannot be kept in secret. All responsible will be held accountable," Francis told the bishops during opening remarks at the seminary. "Those who have survived have become true heralds of mercy. We owe each of them gratitude . . . as they have suffered terrible abuse, sexual abuse."

After that statement, he returned to the theme of much of his visit, extolling the virtues of family life at the center of society and the Catholic church. And he lamented the reluctance of many young people to get married.

"In Buenos Aires, how many women are telling me, 'My son is 30, 34 years old and he's not getting married, I don't know what to do,' and I say 'Don't iron his shirts anymore,' " Francis joked.

He instructed the bishops to help fortify that institution in their pastoral work, going beyond their duties of preaching and praying.

The Sunday morning address to his surrogates, held in the intimate setting of St. Martin's Chapel at St. Charles Borromeo Seminary, built on his speech to attendants at the Festival of Families the night before.

He said the church's shepherds should "accompany and help" young people "mature toward the commitment of marriage."

And he hinted in more ways than one that such ministry "of love" is also in the church's best interests.

"Our ministry needs to be developed in alliance of the church and the family," the pontiff said in Spanish. "To the contrary it will just wilt."

Francis spoke of today's culture of consumerism, loneliness and confusion, which he said sends young people into the escapes of social media and away from commitment and trust.

After the meeting, Cardinal Daniel N. DiNardo, Archbishop of Galveston-Houston and vice president of the U.S. Conference of Catholic Bishops, told reporters that Francis' message about sexual abuse was "very clear" and concrete.

"There's a good deal of work already going on in our church" on dealing with abuse, DiNardo said. "The pope was clear in what he sees is necessary to do."

The meeting with bishops is the first event on the pope's final day in the United States.

After the meeting, seminarians sang to Francis as he left the seminary and boarded a helicopter to Curran-Fromhold Correctional Facility.

The pope concluded his visit with inmates just after 11 a.m. He is expected to spend time the next several hours preparing for the signature event of his trip to Philadelphia: a celebration of Mass as part of the World Meeting of Families at 4 p.m.

That event is expected to draw more than a million people.

After the Mass, Francis will travel to Philadelphia Airport for a farewell ceremony. He is scheduled to depart for Rome at 8 p.m. Sunday, ending a nine-day visit to Cuba and the United States.

-- With Candice Ruud