Pope Francis has acknowledged that the Catholic Church was slow to address the sex abuse crisis, including its widely criticised but not publicly acknowledged practice of moving priests who had abused children to other churches instead of reporting them to the police, saying "the church's conscience came a bit late".

The Pope gave off-the-cuff remarks to a commission he created to tackle the issue, acknowledging the slow pace of church trials and an overall lack of awareness of the problem inside St Peter's walls.

"Paedophilia is a sickness," Pope Francis said. "Today one repents, moves on, we forgive him, then two years later he relapses. We need to get it in our heads that it's a sickness."

The Pope announced he would do away with Vatican appeal trials for cases where evidence of abuse against minors is proven.

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"If there's evidence, that is final," he said. "Those who're sentenced because of sexual abuses against minors can indeed appeal to the Pope and ask for a pardon, but I've never signed one of those, and I never will," he said. "I hope this much is clear."

The Pope's rationale for doing away with an appeal process - according to Italian news outlets' transcripts of his words - lies in his own experience. Faced with such a case at the very beginning of his papacy, he said he'd opted for "the more benevolent path" instead of defrocking a priest. "After two years, though, the priest relapsed," he said.

A Vatican source confirms that these words convey the Pope's own "personal bitterness, as well as the difficulty of curing [paedophiles], as it was once thought possible, which instead ended up being quite a failure".

The Pope's comments and recent events draw attention to his larger efforts to strengthen the church's fight against abuse, as advocacy groups have called for sweeping changes within the Vatican hierarchy.

Last week, the Catholic Church recalled diplomat Monsignor Carlo Alberto Capella back to the Vatican because US investigators suspected him of crimes involving child pornography. And earlier this year, Cardinal George Pell, one of the most powerful officials in the Vatican, was charged by Australian police for "historical sexual assault offences", and he said he returned to his home country "to clear his name".