Pope Francis says Milan's world's fair, which opens on May 1, can inspire decision-makers to help save the "health of the planet that God entrusted to the care of the human race."

Francis on Saturday praised Expo's theme of exploring ways the planet can feed its people. The exposition, which runs for six months, will highlight modern technologies that Francis says can help guarantee "healthy, safe and sufficient food for all peoples."

Meeting with Italian President Sergio Mattarella at the Vatican, Francis expressed hope Expo would encourage deeper reflection about the environment's deterioration.

Francis is working on an encyclical, a major Vatican position paper laying out church teaching, dealing with the environment. It is expected to be published in the next few months.