Pope Francis has apparently spoken out in defence of marriage as an institution between a man and a woman, hurting the hopes of those who see him as a liberal driving force in the Catholic Church.

Last month the Pope warned Catholics not to fear change following an angry synod backlash against a softening of the Church’s stance towards homosexuality.

But in his address at the opening of a three-day conference on traditional marriage hosted at the Vatican yesterday, Francis called family “an anthropological fact… that cannot be qualified based on ideological notions or concepts important only at one time in history”.

The Humanum conference invites people of different religions to come together and celebrate “complementarity between man and woman in marriage” – the idea that men and women have different but complementary roles that they say are essential to building a strong family.

And though he did not refer to gay unions directly, the Pope said: “It is fitting that you have gathered here to explore the complementarity of man and woman. This complementarity is at the root of marriage and family.”

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Francis said: “Children have the right to grow up in a family with a father and mother capable of creating a suitable environment for the child's development and emotional maturity.

“Today marriage and the family are in crisis,” he continued. “We now live in a culture of the temporary, in which more and more people are simply giving up on marriage as a public commitment.

“The revolution in mores and morals has often flown the flag of freedom, but in fact it has brought spiritual and material devastation to countless human beings, especially the poorest and most vulnerable.”

Pope Francis's comments were interpreted by those in the audience as a declaration in support of traditional marriage. Russell Moore of the US's Southern Baptist Convention said: “Pope Francis made clear that male/female complementarity is essential to marriage and cannot be revised by contemporary ideologies.”

LGBT activists reacted similarly to the speech, with the New Civil Rights Movement's David Badash suggesting it “included many veiled attacks on same-sex marriage”.

Zack Ford, the editor of ThinkProgress, tweeted: “I can't hear about how men and women are 'complementary' without hearing 'gay sex is icky'.”

He added: “Dear Humanum, gay people exist, and we are complementary with the same gender. Just ask us! We'll tell you all about it.”

Gay rights activist and father Jeremy Hooper wrote: “People keep telling me that this Pope is new and different and more accepting. Only thing? Just this morning, at the big marriage and family conference currently underway in Rome, he gave a whole speech about marriage being only one man and one woman and how his peeps need to resist any other form.”

He later tweeted a picture of his daughter, adding: “As Humanum attacks my family, I celebrate the joy of parenting. Of life. Of love.”

In March, Cardinal Timothy Dolan reportedly claimed that the pontiff had paved the way for support of civil partnerships at some point in the future, saying it was time the Church studied same-sex unions “rather than condemning them”.