Geneva: United Nations child protection experts have pushed Vatican delegates to reveal the scope of the decades-long sexual abuse of minors by Roman Catholic priests that Pope Francis called "the shame of the Church".

The delegates, answering questions from an international rights panel for the first time since the scandals broke more than two decades ago, denied allegations of a Vatican cover-up and said it had set clear guidelines to protect children from predator priests.

But members of the UN Committee on the Rights of the Child, and abuse victims attending the session in Geneva, demanded far more transparency on crimes that have rocked the Church, from the United States to Europe and Australia.

"The best way to prevent abuses is to reveal old ones - openness instead of sweeping offences under the carpet," Kirsten Sandberg, chairwoman of the 18-strong UN committee, told the Vatican delegation.