"The criminalization of homosexuality is a problem that cannot be ignored," said Francis, who then cited unnamed statistics according to which 50 countries criminalize LGBT people "in one way or another" and about 10 others have laws including the death penalty for them.
Francis, who made his remarks in response to a reporter's question aboard the plane returning from a two-country trip to Africa, received full backing of his comments from two other Christian leaders on the plane with him.
"This is not right. Persons with homosexual tendencies are children of God. God loves them. God accompanies them ... condemning a person like this is a sin. Criminalizing people with homosexual tendencies is an injustice," Francis said.
Sixty-six U.N. member states continue to criminalize consensual same-sex sexual relations, according to data from ILGA World – the International Lesbian, Gay, Bisexual, Trans and Intersex Association. In several countries where same-sex relations are illegal, punishments can include a possible death penalty.
He noted that the Catholic Church's catechism, or book of teachings, says same-sex attraction is not a sin but homosexual acts are. It also says that LGBT people should not be marginalized.
Francis mentioned his now-famous phase from soon after he became pope in 2013 that he could not judge people with same-sex tendencies who are seeking God. He also noted that while visiting Ireland in 2018 he said that parents could not disown their LGBT children, but had to keep them in a loving family.
The pope made the Africa trip as a peace pilgrimage with Archbishop of Canterbury Justin Welby and Moderator of the General Assembly of the Church of Scotland Iain Greenshields.
Both Christian leaders were on the plane returning from there and participated in the pope's customary news conference with reporters, a first on any papal trip.
Both praised the pope's comments.
"I entirely agree with every word he said there," Welby said, noting that the Anglican communion was itself divided over gay rights and that two resolutions against criminalization of LGBT people "have not really changed many people's minds".
Welby added: "I shall certainly quote the Holy Father. He said it so beautifully and accurately".
Expressing his own support of Francis, Greenshields referred to the Bible, saying:
"There is nowhere in my reading of the four Gospels where I see Jesus turning anyone away. There is nowhere in the four Gospels that I see anything other than Jesus expressing love to whoever he meets and as Christians that is the only expression that we can give to any human being in any circumstance".
Francis repeated that the Catholic Church cannot permit sacramental marriage of same-sex couples but that he supported so-called civil union legislation giving same-sex couples legal protection in issues such as pensions, inheritance and health care.