Pope Francis' top adviser on clerical sex abuse implicitly rebuked the pontiff over his accusations of slander against Chilean abuse victims, saying Saturday that his words were "a source of great pain for survivors of sexual abuse."

Cardinal Sean O'Malley, the archbishop of Boston, said he couldn't explain why Francis "chose the particular words he used."

In an extraordinary effort at damage control, O'Malley insisted that Francis "fully recognizes the egregious failures of the church and its clergy who abused children and the devastating impact those crimes have had on survivors and their loved ones."

Francis set off a national uproar upon leaving Chile on Thursday by accusing victims of the country's most notorious pedophile priest of having slandered another bishop, Juan Barros. The victims say Barros knew of the abuse but did nothing to stop it — a charge Barros denies.

"The day they bring me proof against Bishop Barros, I'll speak," Francis told Chilean journalists in the northern city of Iquique. "There is not one shred of proof against him. It's all calumny. Is that clear?"

The remarks shocked Chileans, drew immediate rebuke from victims and their advocates and once again raised the question of whether the 81-year-old Argentine Jesuit "gets it" about sex abuse.

The scandal over the crimes of the Rev. Fernando Karadima has devastated the credibility of the Roman Catholic Church in Chile, and Francis' comments will likely haunt it for the foreseeable future.

O'Malley's carefully worded critique was remarkable since it's rare for a cardinal to publicly rebuke the pope in such terms. But Francis' remarks were so potentially toxic to the Vatican's yearslong effort to turn the tide on decades of clerical sex abuse and cover-up that he clearly felt he had to respond.

O'Malley headed Francis' much-touted committee for the protection of minors until it lapsed last month after its initial three-year mandate expired. Francis has not named new members, and the committee's future remains unclear.