Pope Francis has called on Europe to return to being "mother Europe" and take in refugees and migrants to ease its low birth rate.

He hinted at criticism of people who choose to remain child free. 

And he revealed that two refugee families have been found and housed in the Vatican itself, as he pledged they would be.

Pope Francis was speaking in an interview with Vatican journalist Aura Miguel of Portugal's Radio Renascença as he prepares to visit Cuba and the United States.

Pope Francis, speaking of the two families now living in the Vatican, said: "Yes, yes, yes, they are already there. And Cardinal Comastri did this, my Vicar General for the Vatican, with him the head of the Almonry, who is Bishop Konrad Krajewski, who works with the people, with the homeless. It's he who made the showers under the colonnade, the barber's service. It's truly wonderful, that he brings people from the street to see the Museums and the Sistine Chapel."

The families would stay in residence "until the Lord wants".

He urged Europe to welcome more migrants. "When there is an empty space, people look to fill it. If a country doesn't have children, migrants come to occupy that place. I think about the level of births in Italy, Portugal, and Spain. I think that it's almost 0 per cent. So, if there are no children, there are empty spaces.

"I mean, this not wanting to have children which, in part - it's my interpretation, I don't know if it's correct - is a little bit the culture of 'wellbeing', no? I heard it in my own family, from my Italian cousins, years ago: 'No, children no. We prefer to travel on vacations or buy a villa, or this or that.' And then, the elderly are left alone. I think that the great challenge of Europe is to return to being mother Europe."

The Pope has previously called on every parish, every religious institution and every monastery welcome a family. He indicated that near-empty convents could even be used to house refugee families.

"A family gives more assurance of stability, a little to avoid infiltrations of another type," he said. "When I speak of a parish welcoming a family, I'm not saying they're going to live at the rectory, at the parish residence, but that the parish community sees to it there is a place, a corner of a school to make a small apartment or, in the worst case, rent a modest apartment for the family, but that they have a roof, to be welcomed, and that they are integrated into the community. And there were many reactions. Many, many, right? There are convents that are almost empty."

Alongside this, religious communities should resist the "temptation of the god of money" when considering what to do with their buildings as vocations decline, or otherwise to join the commercial world properly and pay taxes.

"Some congregations say, 'No, now that this convent is empty, we're going to make a hotel, an albergo, and we can receive people and with this we'll support ourselves or earn money.' Well, if you want to do that, pay taxes. A religious school because it's religious is exempt from taxes but if it works like a hotel then pay taxes like everybody else."

Pope Francis, himself the son of migrants who arrived in Argentina in the wave of 1929, said that by 1932 his parents were left standing in the street, without anything. His grandfather bought a warehouse with 2,000 pesos that he borrowed.

Responding in Spanish to questions in Portugese, he said Europe should welcome refugees in order to compensate for the low birth rate and help population levels increase again. He blamed economic injustice for the crisis.

"We see these refugees, these poor people who are escaping from war, escaping from hunger, but that's the tip of the iceberg. But underlying that is the cause, and the cause is a socio-economic system that is bad, unjust, because within an economic system, within everything, within the world, speaking of the ecological problem, within the socio-economic society, in politics, the person always has to be the centre.

"And today's dominant economic system has removed the person from the centre, and at the centre is the god of money. It's the fashionable god today. I mean, there are statistics."

He said a minority of the world's population had the greatest proportion of the wealth.

He said the world was at war with itself and the earth. "It's destroying the earth, that is, our common home. The environment, the glaciers are melting. In the Arctic, the polar bear goes increasingly northward to survive."

Pope Francis also condemned fundamentalism and false friends in another interview with a radio station in his homeland of Argentina.

He said he had experienced what it was like to be used by so-called friends who had tried to exploit him for their own gain.

Speaing to Marcelo Figueroa at the Buenos Aires radio station FM Milenium, Pope Francis said: "The utilitarian sense of friendship, to see what I can get out of being close to this person and making myself his friend, this pains me. I have felt used by some people who have presented themselves as 'friends' when I may not have seen more than once or twice in my lifetime. They used this for their own gain. But this is an experience which we have all undergone, utilitarian friendship."

Speaking on the eve of his visit to Cuba and the US, which will be followed by his controversial Synod on the Family in Rome, he described fundamentalism as "a transversal darkness which robs us of an horizon, which closes us in convictions."

The Pope, who leads a Church divided between liberal modernisers and conservative traditionalists on issues such as marriage, divorce, birth control and the environment, said: "No religion is immune from its own fundamentalisms. In any confession there will be a small group of fundamentalists, whose work is to destroy in the interests of an idea, not of a reality."

He said "reality" was superior to an idea and fundamentalists were guilty of idolatry.

"Fundamentalists push God away from the companionship of His people. They dis-Incarnate Him, they transform Him into an ideology. Therefore, in the name of this ideological God, they kill, attack, destroy, and calumniate. Practically, they transform this God into a Baal, into an idol."