In his first "Urbi et Orbi" (to the city and the world) message, Francis also called for peace between Israelis and Palestinians, an end to the civil war in Syria, and political solutions to conflicts in several African countries.
The former Cardinal Jorge Bergoglio of Argentina also condemned the "iniquitous exploitation of natural resources" and urged everyone to be "guardians" of creation.
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The USS Indianapolis played a key role in one of the conflict's defining attacks before being struck at midnight by Japanese torpedoes.
The King and Queen of Spain joined mourners at a mass in Barcelona to remember victims of the terror attacks as a police manhunt continues.
Rain spreads further east through the day.