Men with deep-rooted homosexual tendencies should not be admitted to the Catholic clergy, and priests who are gay should be celibate or leave rather than lead a double life, Pope Francis said in a new book.

Francis made the comments in a book-length interview with Spanish priest Fernando Prado called “The Strength of Vocation,” in which he discusses the challenges of being a priest or nun today.

“The question of homosexuality is a very serious one,” he said, adding that those entrusted with training men to be priests must be certain that candidates are “humanly and emotionally mature” before they can be ordained.

"In our societies, it even seems homosexuality is fashionable. And this mentality, in some way, also influences the life of the church," Francis was quoted as telling his interviewer.

Francis is quoted in the book as commenting on a clergyman who had told him that having gays in Catholic religious housing "isn't so grave" because it's "only an expression of affection."