Pope Francis has warned that Europe's refugee crisis is just the "tip of the iceberg," fueled by an "unjust" global economic system forcing hundreds of thousands of people to flee war and poverty in search of better lives.

In an interview with a Portuguese Catholic radio station broadcast Monday, Francis recalled that the Bible requires that strangers be welcomed, though he acknowledged security precautions must be taken.

He said: "It's true that 400 kilometers (250 miles) from Sicily there is an exceedingly cruel terrorist guerrilla group, and it's true there's the danger of infiltration."

Francis repeated his call for parishes to welcome in a migrant family and said two families have been identified to move into Vatican housing. He said they can stay "as long as the Lord wants."