Cuban President Raul Castro on Sunday thanked Pope Francis for brokering the thaw between Havana and Washington and said the pope so impressed him that he might return to the Church, despite being a communist.
The 83-year-old younger brother of Cuba's revolutionary leader Fidel spoke with the pope for nearly an hour - unusually long for a papal meeting - during a visit the Vatican said was strictly private and not a state visit.
Papal audiences on Sundays are extremely rare. Francis made an exception when Castro asked if he could stop in Rome on his way back from Moscow to thank Francis for the Vatican's mediation between the United States and Cuba, Cuban officials said.
Leaving the meeting, Castro told reporters that he thanked the pope for Vatican mediation that led to December's historic resumption of diplomatic relations between the former foes after more than half a century of antagonism.
Later, at a news conference with Italian Prime Minister Matteo Renzi, Castro said he came out of the meeting with the pope "really impressed by his wisdom and his modesty".
Francis, who is due to visit both Cuba and the United States in September, is a member of the Jesuit religious order. Castro joked that "even I am a Jesuit in a certain sense" because he was educated by the Jesuits before the revolution.
"When the pope comes to Cuba in September, I promise to go to all his Masses and I will be happy to do so," he said, adding that he reads all of the speeches of Latin America's first pope, who has made defence of the poor a major plank of his papacy.
"I told the prime minister if the pope continues to talk as he does, sooner or later I will start praying again and return to the Catholic Church, and I am not kidding," he said.
Both of the Castro brothers were baptised as Catholics.
The Church's activities were suppressed for decades after the 1959 revolution. The government began loosening restrictions in the early 1990s. After the late Pope John Paul visited in 1998 Fidel Castro re-instated Christmas as a holiday.
The pope's U.S. trip had been planned for some time before the Vatican announced last month that Francis would stop in Cuba on his way to Washington. Francis is expected to stay in Cuba at least two days, Vatican sources said.
It will be the Argentine pope's first visit to both countries as pontiff. His predecessors John Paul II and Benedict XVI, visited Cuba and met Fidel Castro.
This year, the leader of the world's 1.2 billion Roman Catholics is also due to make trips to Bosnia in June, Ecuador, Bolivia and Paraguay in July, and several African countries towards the end of the year.