"Victims should know that the pope is on their side," the Vatican said in a statement after a devastating US grand jury report published on Tuesday decried a systematic cover-up by the Catholic Church.
"Those who have suffered are his priority, and the Church wants to listen to them to root out this tragic horror that destroys the lives of the innocent," the statement said.
"There are two words that can express the feelings faced with these horrible crimes: shame and sorrow," it said.
The Vatican statement added that the church needed to learn "hard lessons from its past, and there should be accountability for both abusers and those who permitted abuse to occur".
The report is thought to be the most comprehensive to date into abuse in the US church, since The Boston Globe first exposed paedophile priests in Massachusetts in 2002.
But while Tuesday's report led to charges against two priests, one of whom has pleaded guilty, the majority of those responsible are dead and the vast majority of crimes happened too long ago to prosecute, officials said.
The two-year investigation by a grand jury into all but two Pennsylvania dioceses turned up dozens of witnesses and half a million pages of church records containing "credible allegations against over three hundred predator priests."
More than 1,000 child victims were identifiable, but the "real number" was "in the thousands," the grand jury estimated.
Hidden for decades
Victims were often traumatised for life, driven to drugs, alcohol and suicide, the grand jury said. The only recourse was to recommend changes to the law and expose what had happened to make sure such widespread abuse was never repeated.
So far only two new priests are being charged with crimes that fall within the statute of limitations.
The grand jury called for changes in the law that would scrap the statute of limitations for child sex abuse, give victims more time to file civil lawsuits and tighten legislation compelling people to report abuse they find out about.
"Despite some institutional reform, individual leaders of the church have largely escaped public accountability," the report said.
"Priests were raping little boys and girls, and the men of God who were responsible for them not only did nothing; they hid it all. For decades."
Church elders were instead promoted and predator priests allowed to remain in ministries for 10, 20, even 40 years after leaders learned of their crimes as the list of victims got longer and longer, Pennsylvania's Attorney General Josh Shapiro said.
Between 5,700 and 10,000 Catholic priests have been accused of sexual abuse in the United States, but only a few hundred have been tried, convicted, and sentenced for their crimes, according to the watchdog Bishop Accountability.
Since the abuse crisis became public in the 2000s, the US church has spent more than $3 billion in settlements, according to Bishop Accountability.
One estimate suggests up there were 100,000 US victims.
Francis was elected in 2013 and vowed to take a "zero tolerance" approach to clerical sex abuse and rid the Church of the scourge of paedophilia, which has done enormous damage to its standing in many countries.
But his credibility on the issue has been hit by a series of missteps and victims' organisations maintain that the Church remains reluctant to hand paedophile priests over to criminal justice authorities.
Francis has compared sex abuse by priests to participating in a "Satanic Mass", but he has also been accused of being too soft on paedophiles, extending to them a general policy of mercy he is promoting in the Roman Catholic Church.
There are widespread accusations that the Catholic Church ignored and covered up child abuse in countries from Australia to Chile.
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