Pope Francis has celebrated Mass in front of tens of thousands of people in the Cuban capital Havana, on his first visit to the Communist-ruled island. Image: BBC News

President Raul Castro, who is not a Catholic, attended the event in city's iconic Revolution Square.

Later the Pope also met the leader's brother and predecessor, Fidel Castro.

Pope Francis, who is at the start of his Cuba and US trip, has been credited with helping the recent thaw in diplomatic ties between both countries.

After his arrival on Saturday, he hailed improving ties between the two countries as "an example of reconciliation for the whole world".

But he also urged both Cuba and the US to "persevere on the path" of detente.

Mother tongue

Security services were seen arresting at least three people who were shouting and attempting to distribute flyers at the edge of Revolution Square as the Mass got under way.

On his way to the service Pope Francis stopped to greet some of the thousands who had come out to see him.

During his homily he said that "Christians are constantly called to set aside their own wishes and desires, their pursuit of power, and to look instead to those who are most vulnerable".

After the Mass Pope Francis met Fidel Castro at his house in Havana for about 30 minutes. The two men exchanged books as gifts, according the the Vatican.

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At the scene: the BBC's Will Grant

From my vantage point, it's hard to gauge exactly how many people filled the enormous Revolution Square in Havana, but their enthusiasm was clear to everyone watching.

The Pope was greeted by thousands in good voice and high spirits, despite the suffocating Caribbean heat.

It was a rare sight: the iconography of revolution such as the huge cast-iron Che Guevara mural juxtaposed against the images of religion, including a vast huge picture of Jesus Christ. Or Raul Castro embracing Pope Francis.

Once again, it felt like evidence that times are changing on the communist island.

In terms of his homily, the Pope discussed ideas of brotherhood and unity but the more overt political message was aimed not at Cuba, but Colombia.

He urged the Colombian government and the left-wing Farc rebel group to persevere with the talks being held in Havana, saying they could not allow "another failure on the path of peace and reconciliation".

The Pope celebrated Mass in the square which is overlooked by a sculpture of the revolutionary Ernesto "Che" Guevara. Photo: APFrancis urged Cubans to "care for one another" in his words to the assembled crowds. Photo: Getty ImagesThree dissidents were arrested at the edge of the square after attempting to hand out flyers. Photo: AFP

The Mass marked the first time Cubans have been addressed in their mother tongue of Spanish by a Pope - Francis is the first to hail from Latin America.

Cristina Fernandez de Kirchner, president of the Pope's native Argentina, also attended.

It is not clear to what extent - if any - Pope Francis will address in public the issue of political freedom with either Raul or his brother, says the BBC's Julian Miglierini in Havana.

The Pope praised improved co-operation between the Cuban government and the Church on Saturday, but called for the Church in Cuba to have "the freedom and the means" to pursue its mission.

Both his predecessors, Pope John Paul II and Pope Benedict XVI, visited the island during their papacy.

Francis's trip will later take him to the US, which he will also be visiting for the first time since his election.