Pope Francis announced on Monday he would soon meet with a group of sex abuse victims at the Vatican and declared "zero tolerance" for any member of the clergy who would violate a child.

Francis also revealed that three bishops are currently under investigation by the Vatican for abuse-related reasons, though it wasn't clear if they were accused of committing abuse itself or of having covered it up.

"There are no privileges," he told reporters en route to Rome from Jerusalem.

The meeting with a half-dozen victims will mark the first such encounter for the pope, who has been criticized by victims for not expressing personal solidarity with them when he has reached out to other people who have suffered.

Francis said the meeting and a Mass at the Vatican hotel where he lives would take place early next month. A statement from the office of Cardinal Sean O'Malley, the archbishop of Boston who is organizing the encounter, said the date and details hadn't been finalized but that the meeting was expected to take place "in the coming months".

"On this issue we must go forward, forward. Zero tolerance," Francis said, calling abuse of children an "ugly" crime that betrays God.

But David Clohessy, the executive director of the main US victims' group, Survivors Network of Those Abused by Priests, or SNAP, dismissed the upcoming session as "another gesture, another public relations coup" that could prove meaningless.

Clohessy said the pope has shown himself capable of making real change in other areas such as church governance and finance but hasn't done so in dealing with sex abuse by Catholic clergy.

But a US attorney who represents clergy abuse victims hoped the meeting would be "substantive and meaningful" rather than for cosmetic purposes. Attorney Mitchell Garabedian said "meeting directly with victims is the most powerful tool that the pope can use in understanding the ugliness and horror of clergy sexual abuse and why it must be stopped or prevented".

He added that there should be more than one such meeting.