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VATICAN CITY — After Raul Castro paid a call Sunday on Pope Francis at the Vatican to thank him for working for Cuban-U.S. detente — the Cuban president said he was so impressed by the pontiff he is considering a return to the Catholic church's fold.

The pontiff "is a Jesuit, and I, in some way, am too," Castro said at a news conference. "I always studied at Jesuit schools."

"When the pope goes to Cuba in September, I promise to go to all his Masses, and with satisfaction," Castro said. "I read all the speeches of the pope, his commentaries, and if the pope continues this way, I will go back to praying and go back to the church, and I'm not joking."

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Francis welcomed Castro to his studio near the Vatican public audience hall, saying, "Bienvenido" in his native Spanish.

The Cuban president, bowing his head, gripped Francis' hand with both of his, and the two men began private talks. The meeting lasted nearly an hour, as the Argentine-born Francis and Castro spoke in Spanish.

Francis will visit Cuba in September en route to the United States.

Pope Francis meets with Cuban President Raul Castro, right, during a private audience at the Vatican, Sunday, May 10, 2015. Cuban President Raul Castro has been welcomed at the Vatican by Pope Francis, who played a key role in the breakthrough between Washington and Havana aimed at restoring U.S.-Cuban diplomatic ties. L'Osservatore Romano / AP

After leaving the Vatican, Castro, the brother of Fidel, the revolutionary leader who brought the Communists to power in Cuba, gushed with praise for Francis.

It was a startling assertion for the leader of a Communist country, whose crackdown on dissidents in the past had drawn sharp Vatican criticism.

"I am from the Cuban Communist Party, that doesn't allow (religious) believers, but now we are allowing it, it's an important step," Castro said.

— Associated Press