Francis, the head of the Roman Catholic Church, died at 7:35 a.m. at his residence in the Vatican's Casa Santa Marta, Cardinal Kevin Farrell said in a statement.
"Millions of people around the world are mourning the tragic news of Pope Francis’s passing," Zelensky said in a message on X, adding that the pontiff's life "was devoted to God, to people, and to the Church."
Francis "knew how to give hope, ease suffering through prayer, and foster unity," the Ukrainian leader also said in his message.
'He prayed for peace in Ukraine'
"He prayed for peace in Ukraine and for Ukrainians," Zelensky added. "We grieve together with Catholics and all Christians who looked to Pope Francis for spiritual support. Eternal memory!"
Zelensky last met with Francis during a visit to the Vatican in October, according to US broadcaster CNN.
The Ukrainian leader told reporters later that he and Francis had discussed the plight of tens of thousands of Ukrainian children deported to Russia since Moscow’s full-scale invasion, and the need to make every effort to bring them home.
Francis in April 2022 condemned atrocities committed during Russia's war against Ukraine, including "the massacre of Bucha," the town near Kyiv where mutilated bodies of civilians and mass graves were found after the withdrawal of Russian forces.
On the first anniversary of Russia's war, Francis called on Catholics to pray for Ukrainians, saying that "war is destruction," CNN reported.
Top Polish officials have paid tribute to Francis, calling him "a great apostle of mercy" and "a good, warm and sensitive man."
The Polish foreign ministry said that "the Holy Father united the hearts of millions with his kindness."
The pontiff had been battling serious respiratory issues after a bout of double pneumonia earlier this year.
Francis, who became pope in 2013, was admitted to Rome's Gemelli Hospital in mid-February after experiencing difficulty breathing.
He spent 38 days there before returning to his Vatican residence to continue his recovery.
In 1957, in his early 20s, Francis—then Jorge Mario Bergoglio—underwent surgery in his native Argentina to remove part of a lung due to a severe respiratory infection, according to the Vatican News.
In his later years, he frequently struggled with respiratory illnesses. In November 2023, he cancelled a planned trip to the United Arab Emirates due to influenza and lung inflammation, the Vatican News said.
Francis, pictured on February 12. Photo: PAP/Abaca
The pope's death comes just hours after he appeared in St. Peter's Square at the Vatican for Easter Sunday celebrations.
Francis waves from the balcony of St. Peter's Basilica on Easter Sunday. Photo: EPA/ANGELO CARCONI
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Source: IAR, PAP, TVP Info, vaticannews.va