It was the pope's first-ever public acknowledgment of the problem of priests and bishops sexually abusing nuns.
"It's not that everyone does this, but there have been priests and bishops who have", Francis said, according to The Associated Press.
On Tuesday, the pope acknowledged that nuns in the church had been abused by priests and bishops, adding that in one case there had been "sexual slavery" perpetrated by clerics and the founder of a community.
POGGIOLI: Just last month, a top official in the Vatican doctrinal office that handles allegations of clerical sex abuse resigned after a former nun accused him of making sexual advances during confession.
The magazine, Women Church World, noted that the scandal involves a corollary: nuns being forced to abort the priests' children or bear children that the priests refuse to recognize.
Francis was asked about priests who target adult women - the religious sisters who are the backbone of the Catholic Church's education, health care and social service ministries around the globe - and whether the Holy See might consider a similar universal approach to combat that issue. "But it's a path that we have already begun". Reportedly, a representative to more than 500,000 Catholic nuns, the International Union of Superiors General, encouraged its members to report abuse.More news: Haas become first Formula 1 team to unveil vehicle for 2019 season
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"At the time, the sister only told her provincial superior and her spiritual director, silenced by the Catholic Church's culture of secrecy, her vows of obedience and her own fear, repulsion and shame".
The nuns scandal broke as the Catholic church has had to contend with a wave of cases involving paedophile priests in countries worldwide from Ireland and the United States to Australia.
Vatican spokesman Alessandro Gisotti said Wednesday Francis "spoke of "sexual slavery" to mean "manipulation" or a type of abuse of power that is reflected in a sexual abuse".
"His gestures became more and more inappropriate", she said, adding: "But he kept going... until the day he raped me".
He said it was a cultural problem, the roots of which lay in "seeing women as second class".
"There are cases, usually in new congregations and in some regions more than others", he said. Last year, a Kerala nun alleged that Bishop Franco Mulakkal had raped her 13 times between 2014 and 2016. They said that if they receive a report of abuse they will help the person bring the complaint "to the appropriate organizations". "I pretended it didn't happen".
The pope said the trip was "brief but very important", linking it to his 2017 visit to Al-Azhar, Egypt, the highest seat of learning in Sunni Islam, and wrote "a new page in the dialogue between Christianity and Islam and in efforts to promote peace in the world based on human brotherhood".