Pope Francis, a strong advocate of the rights of refugees, said in a new book published on Monday that migration does not pose a threat to Christianity.
"To reject a struggling migrant, whatever his or her religious belief, out of fear of diluting a 'Christian' culture is grotesquely mispresenting both Christianity and culture," he said.
"Migration is not a threat to Christianity except in the minds of those who benefit from claiming it is.
"To promote the Gospel and not welcome the strangers in need, nor affirm their humanity as children of God, is to seek to encourage a culture that is Christian in name only, emptied of all that makes it distinctive."
The pontiff made the comments in "Let Us Dream", a new book written in conversation with British biographer Austen Ivereigh.
The pope, the grandson of Italian emigrants who settled in Argentina, regularly expresses solidarity with migrants who cross the Mediterranean, mourning those who lose their lives and denouncing rich countries that fail to welcome them.
"The dignity of our peoples demands safe corridors for migrants and refugees so they can move without fear from deadly areas to safer ones," he said in the book.
"It is unacceptable to deter immigration by letting hundreds of migrants die in perilous sea crossings or desert treks. The Lord will ask us to account for each one of those deaths."
He condemned leaders who "channel their resentments and hatreds against imagined enemies to distract from the real problems", the 83-year-old pontiff wrote.
"A fantasy of national-populism in countries with Christian majorities is its defence of 'Christian civilisation' from perceived enemies, whether Islam, Jews, the European Union or the United Nations," he said.
"The defence appeals to those who are often no longer religious but who regard their nation’s inheritance as a kind of identity.
"Their fears and loss of identity have increased at the same time as attendance at churches has declined," Francis said.