Irish PM Leo Varadkar on Saturday directly urged the pope to take action against abuses and ensure justice for victims worldwide.
Knock: Pope Francis in Ireland Sunday "begged for God's forgiveness" for the child sexual abuse scandal rocking the church but faced accusations by a former Vatican official that he had personally ignored allegations against senior clergy.
Francis is due to speak in front of some 500,000 faithful in Dublin's Phoenix Park as part of his two-day visit to the former Catholic stronghold of Ireland, as abuse victims and their supporters gathered in a "Stand for Truth" rally in the city centre to demand justice.
During Sunday's address to 45,000 supporters at the rain-soaked Knock shrine in the west of the country, the pope "begged for God's forgiveness" for the "open wound" of the scandal and demanded "firm and decisive" measures to find "truth and justice".
The scandal has dogged the visit, and intensified overnight when a former Vatican envoy to the US accused Francis of personally ignoring sexual abuse claims against prominent US cardinal Theodore McCarrick, who was forced to resign last month.
Archbishop Carlo Maria Vigano wrote in a letter published in the National Catholic Register that he had told Francis of the allegations in 2013, but that he had responded by lifting sanctions imposed on McCarrick by predecessor Pope Benedict.
"He (Pope Francis) knew from at least June 23, 2013 that McCarrick was a serial predator," wrote Vigano," adding "he knew that he was a corrupt man, he covered for him to the bitter end."
The Vatican said it had no comment to make on the claims.
Irish Prime Minister Leo Varadkar on Saturday directly urged the pope to take action against abuses and ensure justice for victims worldwide.
Francis said inaction over "these repellent crimes has rightly given rise to outrage, and remains a source of pain and shame for the Catholic community. I myself share those sentiments".
Francis on Saturday also met eight abuse victims, including a woman assaulted by a priest when she was in hospital aged 13 and a man who was illegally adopted because his mother was unmarried.
In a strongly-worded speech at the start of the pope's visit, Varadkar said the abuses in Ireland were "stains" on the Catholic Church, the state and Irish society as a whole.
"There is much to be done to bring about justice and truth and healing for victims and survivors. Holy Father, I ask that you use your office and influence to ensure that this is done here in Ireland and across the world," he said.
He demanded of Francis "that from words flow actions".
Paul Jude Redmond, who was illegally adopted from a Church-run "Mother and Baby Home" and met the pope on Saturday, said the pontiff appeared "genuinely shocked" by the stories of abuse.
But at a news conference in Dublin on Saturday by the group Ending Clergy Abuse (ECA), victim Mark Vincent Healey said the pope's speech in Dublin was a "total missed opportunity".
"We're still waiting. We're left with uncertain silence. When is he going to act? What is he going to do?"
This is the first papal visit to Ireland since John Paul II spoke in front of 1.5 million people during a visit in 1979.
The Church's role and standing has been badly dented by the abuse scandals and the Irish have shed traditional Catholic mores, voting earlier this year to legalise abortion after approving same-sex marriage in 2015.
The pontiff is in Ireland to close the 2018 World Meeting of Families (WMOF) -- a global Catholic gathering that addressed issues including the treatment of gay people in the Church.
Street vendors in Dublin selling papal souvenirs complained of sluggish trade, as protesters rubbed shoulders with devout Catholics in the streets of the city.
In Tuam, a town in western Ireland not far from Knock, a silent vigil was planned for Sunday in solidarity with victims of "mother and baby" homes -- institutions accused of being punishment hostels for unwed pregnant women.
"Significant quantities" of baby remains found in makeshift graves at the site of one such home in Tuam last year shocked the country.
Multiple probes in Ireland have found Church leaders protected hundreds of predatory priests and former Irish president Mary McAleese revealed this month that the Vatican had sought to keep Church documents inaccessible to government investigators.
The abuse scandals in Ireland are part of a worldwide crisis for the Vatican.
A devastating report earlier this month accused more than 300 priests in the US state of Pennsylvania of abusing more than 1,000 children since the 1950s.