Pope Francis met Cuba's revolutionary leader Fidel Castroon Sunday, hours after warning Cubans to beware the dangers of ideology and the lure of selfishness as their country enters a new era of closer ties with the United States.

Latin America's first pope and Castro, the region's last surviving leftist icon of the 20th century, discussed religion and world affairs at the home of the 89-year-old retired president for about 40 minutes.

Vatican spokesman Father Federico Lombardi said the meeting, which included Castro's wife and other family members, was "very relaxed, fraternal and friendly."

Francis, 78, gave Castro several of his official papal writings, two books on spirituality and a book and CD on the writings of Father Armando Llorente, a priest who taught Castro in Jesuit prep school more than 70 years ago.

Castro, who wore a blue-and-white track suit, gave him a copy of "Fidel and Religion," a 1985 book of interviews with a Brazilian priest which lifted a taboo on speaking about religion in Cuba, then officially atheist.

Francis also went to the Palace of the Revolution for an hour-long private meeting with President Raul Castro, Fidel's 84-year-old younger brother.

Raul Castro, an atheist like his brother, surprised the pope by giving him a sculpture of a life-sized crucified Jesus Christ against a backdrop of fishing nets and oars.

The pope has drawn praise in Cuba for his behind-the-scenes role in supporting negotiations last year that led to a historic rapprochement between the United States and Communist-run Cuba.

His visit is aimed at further improving ties between the government and the Roman Catholic Church and encouraging a more open society in Cuba.

Celebrating Mass before tens of thousands of people in Havana's Revolution Square on Sunday morning, Francis sprinkled his mainly religious homily with criticism of "elitism" and ideology.

"Service is never ideological for we do not serve ideas, we serve people," he said at the Mass, attended by Raul Castro and top members of the Communist government.

Francis spoke beneath massive portraits of revolutionary leaders Ernesto "Che" Guevara and Camilo Cienfuegos built into the facades of state buildings. For the Mass, a similarly giant poster of Jesus Christ was hung nearby.

Later on Sunday, the pope held a rally with young people and met with priests and nuns, putting aside his prepared comments and clearly enjoying the chance to improvise and tell jokes in his native language.

He told the young people to have the courage to think outside the box after hearing one of them say Cuba's youth were united in their desire for "profound change" in the country.

DISSIDENTS BLOCKED

Dissidents complained that Cuban police have detained 30-40 opposition activists to stop them attending papal events, and a Reuters witness said security agents wrestled two men and a woman to the ground near Revolution Square on Sunday morning after they started shouting and tried to hand out flyers.

In what government foes could see as criticism of party bureaucracy, the pope said Jesus' apostles foolishly argued about rank and he compared it to "those who climb the ladder most quickly to take the jobs which carry certain benefits".

Francis also appeared to appeal to Cubans to look after each other as the country faces social changes and new economic opportunities.

He said they should continue to be "at the service of the frailty of your brothers and sisters" and "not neglect them for plans which can be seductive, but are unconcerned about the face of the person beside you".

At the end of the Mass, the pope appealed to Colombia's government and Marxist FARC guerrillas to ensure that nearly three years of peace talks in Cuba are successful in order to end their "long night" of war.

Since arriving on Saturday, Francis has exhorted Cuba and the United States to deepen their detente, and encouraged Cuba to grant more freedom to the Catholic Church, which has in recent years re-emerged as a powerful force after suffering decades of repression.

Francis will fly from Cuba to Washington on Tuesday.