Even while the pope spent his morning with the three men and three women, listening to their stories one by one, several victims' groups blasted the meetings as being "a PR event."
The Vatican quoted Francis as expressing personal ''sorrow" in his homily at the private Mass with the victims for the ''sins and grave crimes" of clerical sex abuse against them.
Francis pledged ''not to tolerate harm done to a minor by any individual, whether a cleric or not."
''All bishops must carry out their pastoral ministry with utmost care in order to help foster the protection of minors, and they will be held accountable," Francis said, according to the English translation of his homily, which was delivered in Spanish.
Many victims, especially in the United States, were outraged when Boston Archbishop Bernard Law, blamed for the cover-ups of abusive priests during his tenure, was given a prestigious post at a Rome basilica instead of being demoted.
"I beg your forgiveness, too, for the sins of omission on the part of Church leaders who did not respond adequately to reports of abuse made by family members, as well as by abuse victims themselves," the pope said Monday. ''This led to even greater suffering on the part of those who were abused and it endangered other minors who were at risk."
''Before God and his people, I express my sorrow for the sins and grave crimes of clerical sexual abuse committed against you. And I humbly ask forgiveness," Francis said in his homily.
Without naming specific cases, Francis noted the abuse caused some victims to resort to addictions or even suicide.
"These deaths of these so beloved children of God weigh upon the heart and my conscience and that of the whole church," he said.
Vatican spokesman the Rev. Federico Lombardi said two Irish, two British and two German victims met with the pope. The six adults who had been sexually abused as youths by clergy met privately for about a half-hour each with Francis at his Vatican residence.
None of the victims wanted to speak with reporters, Lombardi said.
Some abuse survivors not at the meeting said the encounter would likely do nothing about their complaints the Vatican has failed to punish bishops and other prelates who systemically covered up the abuse of minors. A German survivor advocacy spokesman, Norbert Denef, called Monday's meeting ''nothing more than a PR event."
Prior to the meetings Monday, Francis has likely already met one Irish survivor of sex abuse by clergy, Marie Collins. She has spent time at the Vatican this year because she's on a panel set up by Francis to help him deal with the scandals staining the church's reputation in many countries.
Francis' predecessor, Pope Benedict, met several times with abuse victims, starting in 2008.