HAVANA - Pope Francis for the first time issued a mild rebuke to the Castro government on Sunday as he spoke to tens of thousands of people during his first visit to the communist nation, church experts said.

In his homily at a Mass at the Plaza of the Revolution, Francis said, "There is a kind of 'service' which truly 'serves,' yet we need to be careful not to be tempted by another kind of service, a 'service' which is 'self-serving,' " he said.

Among those in attendance were Cuban President Raúl Castro, brother of revolutionary leader Fidel Castro; and Argentine President Cristina Elisabet Fernández de Kirchner.

StoryPope Francis uses shock to get message acrossOpinionKeeler: Question pope's visit won't answerSee alsoSpecial coverage: Pope Francis

"There is a way to go about serving, which is interested in only helping 'my people,' 'our people.' This service always leaves 'your people' outside, and gives rise to a process of exclusion," the pope said.

Longtime Vatican analyst John Allen said those comments and others by the pope represented a mild criticism of the Communist-run island.

"This clearly was a kind of thinly veiled and admittedly fairly gentle critique of the Cuban regime and Cuban social revolution," said Allen, who was at the Mass.

advertisement | advertise on newsday

Referring to the pope's comments that service should never be ideological, Allen said, "For Cubans raised on decades of party indoctrination, they will clearly hear that as a kind of mild rebuke.

"Up until the Mass today, this papal stop has been good news for the Castro regime," Allen said. "I think this is probably the first time when the Castro brothers will come away thinking they have something to chew on."

After arriving around 8:15 a.m. and greeting the crowds in his iconic, bubblelike popemobile, he gave a homily on the importance of humility and selflessness, retelling the Biblical story of Jesus asking his apostles what they had been discussing during their travels. The disciples didn't respond, ashamed to admit they had been arguing about who among them was the most important.

@Newsday

"The history of humanity has been marked by the answer we give to this question," Pope Francis said, in a translation of his prepared remarks. "Far from any kind of elitism, the horizon to which Jesus points us is not for those few privileged souls capable of attaining the heights of knowledge or different levels of spirituality."

Pope Francis used that message to call on Christians around the world to serve others, particularly the poor and vulnerable.

Cuban security officials removed at least three people who were yelling and appeared to be distributing fliers before Pope Francis' Mass. Officials collected the pamphlets the three had been distributing, and the protesters' message was not immediately clear.

Speaking to the people of Cuba, the pope also said in the official translation, "God's holy and faithful people in Cuba is a people with a taste for parties, for friendship, for beautiful things. It is a people which marches with songs of praise. It is a people which has its wounds, like every other people, yet knows how to stand up with open arms, to keep walking in hope, because it has a vocation of grandeur.

"Today I ask you to care for this vocation of yours, to care for these gifts which God has given you, but above all I invite you to care for and be at the service of the frailty of your brothers and sisters. Do not neglect them for plans which can be seductive, but are unconcerned about the face of the person beside you. We know, we are witnesses of the incomparable power of the resurrection, which "everywhere calls forth the seeds of a new world."

advertisement | advertise on newsday

The pope played a role in Cuba's newly thawed relations with the United States.

Many of those in attendance said they spent the night in the plaza, and traveled from throughout the country to be here.

"It's a gift from God and a blessing for the entire country," Barbara Rodriguez Acosta, 61, said in Spanish. She said she took a nine-hour bus ride from the interior of Cuba, arrived in the plaza around 12:30 a.m. and spent the night there in anticipation of the pope's Mass.

Acosta said she has not eaten since 6 p.m. Saturday, when the bus stopped for a food break during the trip. But that did not bother her -- she is so filled with excitement about the pope's Mass.

"It's an opportunity that you can't miss," she said. "I don't care if it rains or there is brutally hot sun -- I'm staying."

advertisement | advertise on newsday

Olga Maria Pozo, 43, who has been waiting in the plaza since 10 p.m. Saturday night, said the pope's visit and Mass were especially important because of the role he has played in helping Cuba and the U.S. re-establish relations.

"It means a lot now because he is mediating between Cuba and United States," she said in Spanish. "It's a blessing for all of the Cuban people. It's a gift from God."

The Mass, which began shortly after 9 a.m., took place against a backdrop of a giant image of fellow Argentine Ernesto "Che" Guevara, which looms nearby on the nation's Ministry of the Interior building to the right of the papal altar.

Towering over the plaza is an obelisk-like monument to Cuban revolutionary hero and Latin American literary icon Jose Martí. The pope referred to Martí in his remarks Saturday.

Before the close of Mass, Pope Francis said he felt compelled to turn his thoughts to Colombia, referring to ongoing talks between that country's government and leftist guerrilla group FARC. The two parties are working on a transitional justice agreement that could change FARC's status from an armed organization to a legitimate political movement.

"May the blood shed by thousands of innocent people during long decades of armed conflict, united to that of the Lord Jesus Christ crucified, sustain all the efforts being made . . . to achieve definitive reconciliation," the pope said in prepared remarks translated by the Vatican.

He continued: "May the long night of pain and violence . . . with the support of all Colombians, become an unending day of concord, justice, fraternity and love . . . so that there may be lasting peace. Please, we do not have the right to allow ourselves yet another failure on this path of peace and reconciliation."

Pope Benedict XVI also held a Mass in the plaza during his visit to the island nation in 2012.

Sunday afternoon, Francis is to meet with Raúl Castro before celebrating vespers -- an evening prayer service -- at the Cathedral of Havana.

Francis is scheduled to conclude his public appearances with a greeting Sunday evening to young people at the Centro Cultural Padre Félix Varela.

With Jennifer Barrios and The Associated Press