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Pope Francis has described Europe's refugee and migrant crisis as the biggest tragedy since World War II.

Francis urged tourists and pilgrims in St. Peter's Square Wednesday during his weekly public audience "not to forget" the problem but instead welcome and help refugees. He also encouraged efforts to integrate them in society.

He said integration should keep in mind "the reciprocal rights and duties of those who welcome and those who are welcomed."

Francis repeatedly urged Europe to do more to help the hundreds of thousands of asylum-seekers and economic migrants who've arrived in recent years.

On Friday, Francis has the opportunity to urge Europe to improve ways to handle the migrant crisis when he addresses leaders of the European Union nations on the eve of a summit in Rome.