Pope Francis has said that homosexual couples should be protected by civil union laws, in what is being seen as some of the clearest language he has used on the rights of gay people.

"Homosexual people have a right to be in a family. They are children of God and have a right to a family. Nobody should be thrown out or be made miserable over it," Francis said in a new documentary "Francesco" by Oscar-nominated director Evgeny Afineevsky.

"What we have to create is a civil union law. That way they are legally covered. I stood up for that," he added.

The pope appeared to be referring to when he was archbishop of Buenos Aires and opposed legislation to approve same sex marriages but supported some kind of legal protection for the rights of gay couples.

Papal biographer Austen Ivereigh said the remarks in the film are some of the clearest language the leader of the Catholic Church has used on the subject since his election in 2013.

The pope, who early in his papacy made the now-famous "Who am I to judge?" remark about homosexuals trying to live a Christian life, spoke in a section of the film about Andrea Rubera, a gay man who with his partner adopted three children.

Mr Rubera said in the film that he went to a morning mass the pope said in his Vatican residence and gave him a letter explaining his situation.

He told Francis that he and his partner wanted to bring the children up as Catholics in the local parish but did not want to cause any trauma for the children. It was not clear in which country Mr Rubera lives.

He said the pope telephoned him several days later, telling him he thought the letter was "beautiful" and urging the couple to introduce their children to the parish but to be ready for opposition.

"His message and his advice was really useful because we did exactly what he told us. It's the third year that they (the children) are on a spiritual path in the parish," Mr Rubera said in the film.

"He didn't mention what was his opinion about my family so (I think) he is following the doctrine on this point but the attitude towards people has massively changed," Mr Rubera added.

The documentary premiered at the Rome Film Festival today.

Ursula Halligan, of the organisation We Are Church Ireland, urged Pope Francis to follow through on his comments.

Speaking on RTÉ's Drivetime, Ms Halligan said she was surprised that he made the remarks "as the Roman Catholic catechism teaches that LGBTI people are objectively disordered and their love intrinsically evil."

She said that if the pope is sincere, she would expect him to follow up with an encyclical spelling out the doctrinal implications of his comments.

Ms Halligan said she warmly welcomed his comments, describing them as "hugely significant".