Pope Francis has triggered anger in Chile after accusing victims of a paedophile priest of slander.
Francis said there was "no proof" for their claims that abuse by Father Fernando Karadima had been covered up by another man, Bishop Juan Barros.
"There is not one single piece of proof against him (Bishop Barros). It is all slander. Is that clear?" the Pope said.
One Karadima victim said the Pope's earlier plea for forgiveness over clerical sex abuse was "empty".
The Pope made his comments on Thursday before celebrating Mass outside the city of Iquique in northern Chile.
"The day someone brings me proof against Bishop Barros, then I will talk," the Pope told journalists.
What is the controversy about?
The Catholic Church suffered a body blow in Chile in 2010 when Father Karadima was publicly accused of molesting several teenaged boys in the capital, Santiago, starting in the 1980s.
In 2011 the Vatican found him guilty of abusing teenage boys and sentenced him to a lifetime of "penance and prayer".
He never faced criminal prosecution in Chile as too much time had passed, but the judge who heard victims' testimony in a year-long investigation described them as "truthful and reliable".
Juan Carlos Cruz, one of the accusers, says Bishop Barros was present when Father Karadima - then the bishop's mentor - kissed and groped him and another boy.
While Bishop Barros has not been accused of abuse, the Pope has been criticised for appointing him bishop of Osorno in 2015. Barros's installation ceremony had to be cut short over protests in the cathedral.
What is the response from accusers?
Mr Cruz was one of the bishop's accusers who was quick to condemn the Pope's stance.
"As if I could have taken a selfie or photo while Karadima abused me and others with Juan Barros standing next to him watching everything," he tweeted.
"These people are absolutely crazy, and @Pontifex (the Pope's Twitter handle) is talking about reparation to the victims. Nothing has changed, and his plea for forgiveness is empty."
Another Barros accuser, James Hamilton, told a news conference the response revealed an "unknown face" of the pontiff.
"What the Pope has done today is offensive and painful, and not only against us, but against everyone seeking to end the abuses," he said.
Pope's defence will raise questions
Analysis by James Reynolds in Rome
Pope Francis began his trip with an uncompromising message: "It is right to ask for forgiveness and to make every effort to support the victims [of abuse committed by priests]."
This makes his subsequent dismissal of claims made against Bishop Juan Barros all the more difficult for victims to understand.
At the heart of this issue lies the Pope's decision to offer his consistent support to the bishop. In 2015, despite opposition in Chile, Francis appointed Juan Barros as the Bishop of Osorno. The Pope was then recorded telling visitors to the Vatican that there was not a shred of evidence that the bishop had covered up crimes committed by a fellow priest. On his trip to Chile, Francis repeated this blunt defence of Juan Barros.
In legal terms, the burden of proof does not lie with the Pope or his bishop to prove the bishop's innocence. But a papacy is also judged in other ways. Some will wonder why the Pope does not offer a more detailed explanation as to exactly why he chooses to believe and defend a bishop against the cover-up allegations made by victims in Chile.
The controversy comes at a time when questions are being asked about the Vatican's efforts to tackle clerical sexual abuse. In 2014, the Pope set up a high-profile commission to advise him. But the two commission members who were themselves survivors of clerical abuse resigned in protest at an apparent lack of progress. At the end of 2017, the commission's term formally expired. Its exact future is unclear.
What other response has there been in Chile?
Another senior Catholic figure in Chile, Bishop Alejandro Goic of Rancagua, criticised Bishop Barros's continuing role in the Church, telling T13 radio: "It left me with a bitter taste that a brother of mine occupied a leading role [in the abuse scandal] that was not good."
He added: "The victims are the priority, they should be the main concern of the Church."
The state co-ordinator for the Pope's visit to Chile, Benito Baranda, told Radio Cooperativa that Bishop Barros "should have stopped being a bishop a long time ago" and that his presence was damaging the Church.
Writing in La Tercera newspaper, journalist Ascanio Cavallo said the Pope's stance could "multiply the wrath" of those who want to see the bishop expelled from his post, but added: "There is no longer any doubt: the Pope supports his bishop.
Earlier in his Chile trip, Francis had met victims of sexual abuse by priests in the country. He cried with them and said he felt "pain and shame" over the scandal.
The US-based NGO Bishop Accountability says almost 80 members of Catholic clergy have been accused of child sex abuse in Chile since 2000.
Pope Francis arrived in Peru late on Thursday for a three-day visit which will conclude his two-nation South America trip.