Pope Francis has promised concrete action to tackle child sex abuse at the end of a Roman Catholic Church summit on paedophilia.
Clergy guilty of abuse were "tools of Satan", the Pope said, pledging to face every case with "utmost seriousness".
Child sex abuse, he said, reminded him of the ancient religious practice of child sacrifice in pagan rites.
Bishops would now review and strengthen their guidelines to prevent abuse and punish perpetrators, he added.
"I am reminded of the cruel religious practice, once widespread in certain cultures, of sacrificing human beings - frequently children - in pagan rites," he said at the end of a four-day summit held in the Vatican.
"The inhumanity of the worldwide phenomenon becomes even more serious and more scandalous in the Church, because it is in contrast with its moral authority and its ethical credibility.
"The consecrated person, chosen by God to guide souls to salvation, lets himself be subjugated by his own human frailty, or by his own illness, thus becoming a tool of Satan. In the abuses, we see the hand of evil that does not spare even the innocence of children."
He said victims would now be the priority and promised an end to cover-ups, saying all abusers would be brought to justice.
He also stressed child sexual abuse was a universal problem - "a widespread phenomenon in all cultures and societies".
The unprecedented conference - called Protection of Minors in the Church - was attended by the heads of all national bishops' conferences from more than 130 countries.
They were handed a roadmap of suggestions on how to handle abuse, such as drawing up mandatory codes of conduct for priests, training people to spot abuse and informing police.
Those gathered at the Vatican also heard testimonies from victims - who mostly remained anonymous - telling stories of abuse and cover-up.
One woman from Africa said she had been forced to have three abortions after being abused for years as a teenager by a priest who refused to use contraception.
Another victim from Asia said he had been molested more than 100 times.
When he was elected in 2013, he called for "decisive action" on the issue, but critics say he has not done enough to hold to account bishops who allegedly covered up abuse.
Thousands of people are thought to have been abused by priests over many decades, and the Church has been accused of covering up crimes around the world.
Survivors say new safeguarding protocols are needed to protect minors.
Pope Francis is under serious pressure to provide leadership and generate workable solutions to what is the most pressing crisis facing the modern Church - one which some say has left its moral authority in tatters.