Pope Francis on Sunday described clergy who abuse kids as "tools of Satan" and compared the sexual abuse of children to human sacrifice as he addressed the Catholic Church's top bishops at the end of a landmark summit to tackle paedophilia.

"I am reminded of the cruel religious practice, once widespread in certain cultures, of sacrificing human beings – frequently children – in pagan rites," he said.

The Pope said even a single case of abuse is an "atrocity" and said the Church will spare no effort to bring abusers to justice.

Before the Pope's speech, a leading archbishop said on Sunday the Catholic Church has become its "own worst enemy" for concealing clergy sexual abuse and not listening enough to victims.

"We will not go unpunished," Archbishop Mark Coleridge of Brisbane, Australia said in the homily of a final Mass ending the four-day conference convened by Pope Francis to confront a worldwide scandal.

On Saturday, a nun and a woman journalist addressed the conference to deliver tough criticism of Church, accusing them of hypocrisy and covering up horrendous crimes against children.

After the conference, the Vatican says it will formulate follow-up measures to make sure all bishop return home knowing how to put anti-abuse procedures into place. With reports by Reuters and Agence France-Presse