Pope Francis has publicly acknowledged the scandal of priests and bishops sexually abusing nuns.
Francis, who also said there had been one case where sisters had been reduced to "sexual slavery", vowed to do more to fight the problem.
The Pope admitted to the problem for the first time in public during a conference while returning to Rome from the United Arab Emirates.
The acknowledgement comes just two weeks before he hosts an unprecedented gathering of bishops to craft a global response to the scandal of priesthood predators who targeted children and the superiors who covered up the crimes.
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.
"It's not that everyone does this, but there have been priests and bishops who have," Francis told reporters. "And I think that it's continuing because it's not like once you realise it that it stops. It continues. And for some time we've been working on it.
"Should we do something more? Yes. Is there the will? Yes. But it's a path that we have already begun," Francis said.
His acknowledgement of the problem comes as he prepares to decide the fate of the disgraced American ex-cardinal, Theodore McCarrick, who is accused of abusing minors as well as adult seminarians.
Francis noted that Pope Benedict XVI had taken action against a France-based order that admitted the priest who founded it had violated his chastity vows with his female recruits.
Francis said the sisters had been reduced to "sexual slavery" at the hands of the Reverend Marie-Dominique Philippe and other priests.
The Community of St Jean admitted in 2013 that Philippe had behaved "in ways that went against chastity" with several women in the order, according to the French Catholic newspaper 'La Croix'.
Francis's comments about "sexual slavery" suggested the relations were not consensual and could have involved abuse of conscience and power. He said Benedict acted "because a certain slavery of women had crept in, slavery to the point of sexual slavery on the part of clergy or the founder".
"Sometimes the founder takes away, or empties the freedom of the sisters. It can come to this," Francis said.
Later, the Vatican moved to clarify his comments, saying he was referring to an abuse of power that was reflected in instances of sexual abuse.
Vatican spokesman Alessandro Gisotti said Francis "spoke of 'sexual slavery' to mean 'manipulation' or a type of abuse of power that is reflected in a sexual abuse".
Pope Francis urged religious leaders yesterday to work together to reject the "miserable crudeness" of war as he opened the first-ever papal visit to the Arabian Peninsula, the birthplace of Islam, with a strong denunciation of violence committed in God's name.