Francis was greeted by President Raul Castro at Jose Marti International airport in Havana, where the pontiff urged Cuba to grant its people the "freedom, the means and the space" to practice their faith, an implicit criticism of the many restrictions the country places on religion.

The Catholic Church was once an integral part of Cuban history, the Pope said, inspiring veterans of its war for independence and "sustaining the hope which preserves people's dignity in the most difficult situations."

In his short speech, Francis also invoked Jose Marti, a Cuban hero, to deliver a veiled critique of the Castros, said Andrew Chesnut, a professor of Latin American history at Virginia Commonwealth University. Marti, a George Washington-type figure, died in 1895 during the war for independence.

"He specifically referenced Marti as a fighter against 'dynasties,' a reference of course to the five decadelong Castro regime," Chesnut said.

But a Vatican spokesman, the Rev. Federico Lombardi, said the Pope was not necessarily referring to the Castros.

"I don't think that it was a citation chosen for a specific reference to today's situations," Lombardi said at a Saturday evening news conference.

Francis has criticized Cuba in the past, though, writing in a 1998 book that its "authoritarian" and "corrupt" regime should be scrapped in favor of a representative democracy.

Francis is the third pontiff to visit Cuba, after Saint John Paul II in 1998 and Benedict XVI in 2012. Francis' call for Cuba to "open itself" to the world echoed John Paul's remarks, a sign of the Catholic Church's longstanding efforts to carve out space in a country that has been officially atheist for decades.

Lombardi said the Pope believes religious freedom in Cuba means more than the ability to worship freely. It also entails the right to open schools and practice acts of charity, as well as other missions.

5 key questions about the Pope's trip to Cuba, United States

Castro, who has said the Pope has inspired him to consider joining the Catholic Church, effusively praised the pontiff on Saturday, particularly his criticism of consumerism and environmental degradation. He also thanked Francis for his role in restoring ties between the United States and Cuba, while calling for the closing of the U.S. military base on Guantanamo Bay.

On Tuesday, the Pope will fly to Washington, a visible sign of the detente he has helped broker between Cuba and the United States.

"For some months now, we have witnessed an event which fills us with hope," the Pope said. "The process of normalizing relations between two peoples following years of estrangement."

Francis also called the restoration of diplomatic ties "an example of reconciliation for the entire world."

"The world needs reconciliation in this environment of 'Third World War by stages' that we are experiencing."

Some American conservatives, however, have criticized the restoration of ties with the communist country, saying that the United States should have required the release of political dissidents.

"The Castro brothers are mass murderers," Rep. Chris Smith, a Republican from New Jersey, told CNN. "They have tortured and imprisoned thousands of dissidents."

Pope Francis' schedule for U.S., Cuba

President Barack Obama and Raúl Castro spoke on the phone Friday to discuss the process of normalizing relations between the two countries.

Just this week, the United Nations announced that Raul Castro would travel to New York to attend the U.N. General Assembly. It will be his first visit to the United States in more than a half century.

U.S. and Cuban officials have said that Obama could visit the communist-run island next year, if the two countries progress sufficiently in normalization talks.

Earlier Friday, the departments of Treasury and Commerce announced revisions to existing Cuban sanctions, in what is the third set of regulatory changes since the President announced that the United States would re-establish diplomatic relations with Cuba in December.

Rubio: Will Francis visit inspire freedom in Cuba?

CNN's Patrick Oppmann contributed to this report.