PANAMA CITY - US President Barack Obama and Cuba's Raul Castro will have a historic face-to-face encounter at the Summit of the Americas this week, breaking the ice after decades of glacial relations.
The image of US and Cuban presidents sitting across from each other at the 35-nation summit for the first time after decades of Cold War-era animosity will be the highlight of the gathering in Panama on Friday and Saturday.
While the meeting will mark a major milestone - no Cuban leader has attended a Summit of the Americas - the two sides have yet to reopen embassies and lingering differences have been evident at negotiations that started in January.
A major sticking point has been Cuba's inclusion on a list of state sponsors of terrorism.
The White House indicated this week that the State Department was in the "final stages" of deciding whether to recommend Havana's removal from the list, and that Congress would then have 45 days to decide whether to override the decision.
"We're trying to get it done quickly," a US State Department official told AFP on condition of anonymity.
In another sign of warming ties, the US State Department said Secretary of State John Kerry could meet with Cuban Foreign Minister Bruno Rodriguez on the sidelines of the summit.
One wildcard is Venezuela's leftist President Nicolas Maduro, Havana's main ally in the region, who could overshadow the summit with grievances over US sanctions against Caracas officials over an opposition crackdown.
Maduro plans to bring a petition with 10 million signatures from Venezuelans demanding that Obama remove the executive order declaring Venezuela a national security threat.
"The Obama-Castro meeting will still punch through as the highlight, but certainly (Venezuela) will complicate that story and weaken it," Ted Piccone, a foreign policy advisor during the Bill Clinton presidency, told AFP.
Maduro's petition could "become a major polarizing issue at the summit," said Piccone, now an expert at the Brookings Institution think tank.
The White House is seeking to ease tensions, saying it does not really believe that Caracas threatens US national security, and sending a senior official to meet with Venezuelan officials in Caracas.
Senior State Department official Thomas Shannon met Wednesday with Venezuelan Foreign Minister Delcy Rodriguez, whose office said that she demanded again that Obama withdraw his executive order.
Separately, the Brazilian government said President Dilma Rousseff spoke with Maduro, who expressed "his willingness to promote a reduction of tensions with the United States on the basis of mutual respect of national sovereignty." Brasilia said Maduro had spoken with US Vice President Joe Biden by telephone.
Castro and other Latin American leaders have defended Venezuela.
But "neither the United States nor Cuba will let Venezuela insert itself in this process in any way," said Frank Mora, a Latin America expert at Florida International University and former Pentagon official.
From Eisenhower to Obama
All eyes will undoubtedly be on how Obama and Castro interact during the summit.
The last substantive talks between US and Cuba leaders was also in Panama in 1956, when President Dwight Eisenhower met with Fulgencio Batista, who was toppled by Fidel Castro three years later.
For Obama, the gathering comes on the heels on last week's tentative nuclear accord with Iran, another historic US foe.
For Castro, it marks another milestone amid modest economic reforms that he has implemented in Cuba since taking over for his brother Fidel after an illness in 2006.
Obama and Castro briefly shook hands at Nelson Mandela's memorial service in Johannesburg in 2013, and they spoke by telephone before their December announcement that they would seek to restore full diplomatic ties.
White House officials say that while the two leaders will have a chance to meet, they may not sit down for a formal bilateral get-together.
Their negotiators, meanwhile, have met several times since January for complex talks to reopen embassies that closed in the 1960s, with the US demanding that its diplomats get unfettered access to ordinary Cubans.
"When you have two countries that haven't really spoken to each other like this in over 50 years, you have a lot of issues to work through as you aim to open up embassies," said White House aide Ben Rhodes.