Pope Francis has declined to comment on a claim he personally ignored sexual abuse allegations against a senior clergyman, after a visit to Ireland dominated by Church scandals.
Archbishop Carlo Maria Vigano, a former Vatican envoy to the United States, said he had told Francis of the allegations against prominent US cardinal Theodore McCarrick in 2013.
But rather than punish McCarrick, who was forced to resign last month, Vigano said Francis had lifted sanctions imposed on him by his predecessor Pope Benedict XVI.
Vigano called on Francis to resign in a letter published Saturday in the National Catholic Register.
He said the pope "knew from at least June 23, 2013, that McCarrick was a serial predator," adding that "he knew that he was a corrupt man, he covered for him to the bitter end".
But the pope refused to address the brewing scandal on Sunday.
"I will not say a word about that. I think that the communique speaks for itself," Francis said on his plane as he flew back from Dublin to Rome.
He had "begged for God's forgiveness" for past clerical abuse scandals during his landmark trip to Ireland, where they have badly damaged the image of the Catholic Church.
He said he was demanding "firm and decisive" measures to find "truth and justice".
'Nope to the pope'
Before 45,000 supporters at the rain-soaked Knock shrine in the west of Ireland on Sunday, the pope spoke of the "open wound" of the scandals.
He later said mass to tens of thousands of flag-waving worshippers before heading back to Rome after his two-day visit.
He also acknowledged other abuses by the Irish church, including at its so-called "mother and baby" homes for unwed mothers.
In the Irish capital, about 5,000 abuse victims and supporters braved the weather to attend a "Stand for Truth" rally.
A woman dressed as a nun, with fake blood on her hands, and a man handing out homemade placards reading "The church protects pederasts" were among those protesting.
It was the first papal trip to Ireland since John Paul II spoke in front of 1.5 million people during a visit in 1979.
"I think it's obviously causing quite a lot of distress," abuse victim and campaigner William Gorry said of the visit.
"Healing is something that's going to take a long, long time if it's going to happen at all," he told AFP.
At another "Nope to the Pope" demonstration, protesters called for gay and transgender recognition, a clearer separation of religion and state in Ireland and the acceptance of contraception by the Vatican -- as well as action on abuse.
The pope went to Ireland to close the 2018 World Meeting of Families -- a global Catholic gathering that addressed issues including the treatment of gay people in the Church.
On the plane back to Rome, the pope recommended parents seek psychiatric help for children who show homosexual tendencies.
"When it shows itself from childhood, there is a lot that can be done through psychiatry, to see how things are. It is something else if it shows itself after 20 years," he said.