Pope Francis met with Fidel Castro Sunday at the Cuban revolutionary leader's home in Havana after an outdoor mass attended by hundreds of thousands of people on the city's iconic Revolution Square.

In what is sure to become an emblematic moment of Francis' tour of Cuba and the United States -- the Cold War enemies whose reconciliation he helped to bring about -- the pope chatted with the 89-year-old Castro and his family for about 30 or 40 minutes, said Vatican spokesman Federico Lombardi.

With tense bilateral ties recently renewed after five decades, and top U.S. diplomat John Kerry due in Havana in days, Cuba briefly detained about 90 activists on Sunday.

Cuban security forces rounded up about 50 protesters with the Ladies in White dissident group and around 40 other activists, some wearing masks with the image of U.S. President Barack Obama, according to an Agence France Presse reporter.

Colombia's Marxist FARC rebels, now negotiating a peace deal in Havana, said Sunday they hope to meet with Pope Francis on his upcoming Cuba visit.

Pope Francis will visit Cuba September 19 to 22 as part of a tour that will later take him to the United States.

At the U.S. mission in Havana, there were few outward signs Monday of its new status as an American embassy and the epochal shift in relations with Cuba after a 54-year break.

The former US Interests Section became an embassy just after midnight, but no U.S.flag will fly over the building on Havana's waterfront Malecon until U.S.Secretary of State John Kerry visits August 14.

The United States and Cuba have reached a deal to reopen embassies in Washington and Havana, in a major step toward ending decades of Cold War enmity.

President Barack Obama is expected to issue a statement at 11:00 am (1500 GMT) Wednesday in the White House Rose Garden about the deal, which constitutes one of the major foreign policy achievements of his presidency.

Colombian President Juan Manuel Santos said Thursday he welcomes international pressure to accelerate peace talks with the FARC guerrillas, which has mounted in recent weeks as fighting has intensified.

The international community has voiced alarm over Santos's decision in April to resume air strikes on the Revolutionary Armed Forces of Colombia (FARC), a move that prompted the rebels to scrap a unilateral ceasefire they had declared in December.

President Barack Obama on Monday nominated Roberta Jacobson, a key figure in ongoing talks with Cuba, to be the next ambassador to Mexico.

Jacobson traveled to Havana in January, becoming the most senior ranking official to visit the communist island in 35 years.

As Cuba and the United States work on thawing ties, a group of U.S. lawmakers voiced optimism in Havana Wednesday that the U.S. economic embargo against Cuba could be lifted.

Led by Senator Tom Udall, the group of Democratic lawmakers was on a mission in an attempt to strengthen ties between the former Cold War foes following decades of enmity.

Colombia's smaller insurgency, the National Liberation Army (ELN), has met with members of the main rebel force FARC, in Cuba, with the blessing of President Juan Manuel Santos, who is hoping it will lead to a second peace process.

The goal of the discussion, Santos said Monday, was "to make progress in our drive to put an end to more than 50 years of armed conflict" that has pitted the Marxist FARC and leftist ELN against the government and right-wing paramilitaries.

French President Francois Hollande called Monday for an end to the US embargo on Cuba, during the first visit by a Western leader to the island since Washington and Havana moved to restore ties.

Addressing the half-century-old trade embargo ahead of meetings with Fidel and Raul Castro, the brothers who have ruled Cuba since its 1959 revolution, Hollande said France will do whatever possible to see that "the measures that have so badly harmed Cuba's development can finally be lifted, repealed."