WASHINGTON - Pope Benedict XVI spoke Thursday with victims who as children were sexually abused by their priests, an unexpected gathering that was the Roman Catholic Church's most dramatic step yet to acknowledge the harm caused by the clergy.

The unscripted meeting at the Vatican Embassy was facilitated by Boston Cardinal Sean O'Malley and involved victims from the Boston area, viewed as the seat of the widespread scandal, which involved 12,000 children and teenagers being violated by 5,000 priests in Catholic parishes nationwide.

"They prayed with the holy father, who afterward listened to their personal accounts and offered them words of encouragement and hope," said a statement from the Rev. Federico Lombardi, a Vatican spokesman.

Three of the participants spoke emotionally about the meeting in an interview on CNN, each saying that he or she drew hope and some optimism from it.

"I basically told him I was an altar boy in the sacristy praying to God, ... and it wasn't just sexual abuse, it was spiritual abuse," Bernie McDaid said.

Victim Olan Horne said victims were allowed to tell the pope anything they wanted. He said that he didn't think he needed another hollow apology from the church, but that the pope showed sincere regret and offered him hope.

"I got up to him, and I burst into tears," said Faith Johnston. "I think my tears alone spoke so much."

The pope hasn't shied away from the issue since he left Rome on his first trip to the United States since ascending to the papacy three years ago. First, en route on the papal plane Tuesday, he acknowledged the scandal as a shameful episode in the church's history in an interview with reporters. Then, in a speech to bishops Wednesday, he told them to reach out to victims of the "gravely immoral behavior."

And Thursday, as he celebrated Mass for 45,000 people in a baseball stadium turned open-air cathedral, he acknowledged the scandal as well. The meeting with victims came after that.

Victims' advocates called Thursday's meeting and Benedict's comments progress, but they said they fell far short of what the pope must do to address the abuse.

"It's easy to give a sermon about this," said Terry McKiernan, the president of BishopAccountability.org of Massachusetts. "It's a little harder to face a victim who's been raped by one of your employees and listen to him and say you're sorry. But the really hard part comes when you start doing something about it."

The somber admissions by the church were made against an otherwise joyful celebration of the pope's six-day trip to the United States.

At the Mass earlier Thursday, the leader of the world's 1 billion Roman Catholics -- 67 million of them in the United States -- celebrated a song-filled service rich with tradition.

The Nationals Park baseball stadium was transformed for the Mass, with the altar constructed in the outfield; hundreds of priests in red, white and black robes on the field; and thousands of worshippers waving gold-and-white papal flags from the stands.