VATICAN CITY, Holy See -- Pope Francis risked the ire of the world's childless dog and cat owners Wednesday, suggesting people who substitute pets for kids exhibit "a certain selfishness.”

Speaking on parenthood during a general audience at the Vatican, Francis lamented that pets "sometimes take the place of children" in society.

"Today... we see a form of selfishness," said the Pope. "We see that some people do not want to have a child.

"Sometimes they have one, and that's it, but they have dogs and cats that take the place of children. This may make people laugh but it is a reality."

The practice, said the head of the world's 1.3 billion Catholics, "is a denial of fatherhood and motherhood and diminishes us, takes away our humanity".

Thus, "civilisation grows old without humanity because we lose the richness of fatherhood and motherhood, and it is the country that suffers", the pontiff said at the Paul VI Hall.

Pope Francis has been photographed petting dogs, allowed a baby lamb to be draped over his shoulders during Epiphany in 2014 and even petted a tiger and a baby panther.

But while his predecessor, Benedict XVI, was a cat lover, Pope Francis is not known to have a pet at his Vatican residence.

Italy's International Organization for the Protection of Animals (OIPA) said it was "strange to think that the pope considers the love in our lives limited quantitatively" while citing the sacrifices of volunteers who save the lives of animals.

"It is evident that for Francis, animal life is less important than human life. But those who feel that life is sacred love life beyond species," said OIPA President Massimo Comparotto in a statement.

- Kids are hard -

In 2014, Pope Francis told Il Messaggero daily that having pets instead of children was "another phenomenon of cultural degradation", and that emotional relationships with pets was "easier" than the "complex" relationship between parents and children.

On Wednesday, while inviting couples who are unable to have children for biological reasons to consider adoption, he urged potential parents "not to be afraid" in embarking on parenthood.

"Having a child is always a risk, but there is more risk in not having a child, in denying paternity," he said.

The Argentine pontiff has in the past denounced the "demographic winter", or falling birth rates in the developed world.

Earlier this year, he criticised modern society, in which career and money-making trumps building a family for many, calling such mentality "gangrene for society".