Panama City (AFP) - On the eve of an historic meeting with Raul Castro, US President Barack Obama pointedly met two of the Cuban leader's fiercest critics and launched a staunch defense of opposition activists Friday.
In a move that could irritate Havana, Obama held a closed-door discussion with dissident lawyer Laritza Diversent and political activist Manuel Cuesta Moura, along with a dozen other activists from the Americas.
The meeting came just hours before a head to head with Castro that will hail the symbolic end of US-Cuba antagonism that began over five decades ago.
Obama and Castro will join some 30 other regional leaders at the Summit of the Americas in Panama for a dinner on Friday, before the two hold talks on Saturday.
Before the summit, Obama addressed a large group of civil society activists from across the region.
While declaring that the days of US meddling in the region were over, the first African American president of the United States launched a defiant and markedly personal defense of Washington's support for opposition groups.
"We've stood up, at great cost, for freedom and human dignity, not just in our own country, but elsewhere. I'm proud of that," Obama said, citing the US civil rights movement.
"As you work for change, the United States will stand up alongside you every step of the way."
Turning to Cuba, Obama said that even as "a new chapter" in relations was launched, "we'll have our differences, government to government, with Cuba on many issues."
- Dinner first -
Obama, Castro and other regional leaders will sit down for a seaside dinner in a complex of ruins from the era of the Spanish conquistadors.
US officials said Obama and Castro's expected meeting will take place on Saturday, sealing their historic announcement on December 17 that their countries would restore ties severed since 1961.
"We certainly do anticipate that they will have the opportunity to see each other at the summit tomorrow, to have a discussion," senior Obama advisor Ben Rhodes told reporters.
He said the extent of the meeting had yet to be decided, but that the two leaders will "take stock" of the negotiations to normalize relations and reopen embassies, as well as discuss lingering "differences."
The US and Cuban chief diplomats, Secretary of State John Kerry and Foreign Minister Bruno Rodriguez, made history themselves late Thursday when they held the highest level talks since 1958.
Obama and Castro briefly shook hands at Nelson Mandela's funeral in December 2013.
An actual discussion would be the first substantive talks between US and Cuban leaders since 1956, when President Dwight Eisenhower met dictator Fulgencio Batista, who was toppled by Fidel Castro three years later.
Rhodes said Obama and Castro had already discussed the ongoing negotiations and the upcoming summit by telephone Wednesday -- their second phone call since December.
But he said there was no decision yet on one of the key obstacles in the negotiations, Cuba's presence on the US blacklist of state sponsors of terror.
"I'm not ruling out any announcement but... we are not there yet in terms of a final recommendation being made to the president, and the president making a determination," Rhodes said.
Cuba's presence on the blacklist -- which also includes Iran, Sudan and Syria -- has been a major sticking point in negotiations to reopen embassies.
If Obama decides to remove Cuba from the list, Congress will have 45 days to decide whether to override his recommendation.
Cuba has other major demands, most importantly that the US Congress lift an embargo that the communist regime blames for the island's economic troubles.
Washington wants Cuba to end restrictions on the movement of its diplomats on the island, giving them unfettered access to ordinary Cubans.
- Venezuela question -
Opinion polls show the reconciliation is backed by majorities of Americans and Cubans, though some US lawmakers have been very critical.
But Cuban government supporters confronted dissidents on the sidelines of the summit, heckling them as they attended a civil society forum.
And even as Obama moves to remove an old source of tension in US relations with Latin America, a new headache has emerged since he imposed sanctions against Venezuelan officials accused of human rights abuses in an opposition crackdown.
Venezuelan President Nicolas Maduro, Havana's main ally in the region, will bring a petition with 13.4 million signatures urging Obama to lift his executive order.
Maduro received a hero's welcome as he arrived at a rally with a hundreds of supporters in Panama City's El Chorillo monument, built for victims of the 1989 US military invasion to oust Manuel Noriega.
Maduro vowed to hand Obama a letter of victims demanding reparations.
"We must have justice," he said. "The United States must ask forgiveness from Panama and Latin America for the invasion."
But Washington is seeking to ease tensions, dispatching a senior official this week to meet with Maduro in Caracas.