US President Barack Obama on Tuesday shook hands with Raul Castro, leader of long-time Cold War foe Cuba, at the memorial service in South Africa for Nelson Mandela.
Obama offered the handshake before taking the stage to give his speech at the ceremony, in a new sign of his willingness to reach out to US enemies, a US official told AFP.
The United States maintains a five-decade-old embargo against the communist island nation, which Havana says has cost the economy $1.1 trillion.
The handshake was seen by millions around the world watching the memorial being broadcast live and comes as Obama tries to make good on his vow to reach out even to the most implacable of US foes.
In September, the US leader spoke by telephone with Iranian President Hassan Rouhani, in the first such gesture since the 1979 revolution in the Islamic republic.
Cold War foes Cuba and the United States have had only limited ties for half a century, most of it under the iron fist rule of Raul's brother Fidel Castro.
Washington has maintained a trade embargo against Cuba for half a century, and the fate of the communist state is a bitter issue in US domestic politics.
Vehemently anti-Castro Cuban-Americans make up a sizable portion of voters and political donors in Florida, a battleground state where US presidential elections can be won or lost.
As a presidential candidate Obama was pilloried as naive and dangerous by rivals from both parties for suggesting that as president he would be willing to talk to foes without preconditions.
Obama's ability to track down and kill Osama bin Laden and a series of drone strikes has largely insulated him from allegations of weakness in foreign and security policy, but the president was careful to pointedly call out oppressive leaders in his speech Tuesday, with Castro just feet away.
"There are too many leaders who claim solidarity with Madiba's struggle for freedom, but do not tolerate dissent from their own people," he said, stabbing his finger in the air.
It is unclear if Tuesday's gesture will significantly thaw relations. In 2000, then President Bill Clinton shook the hand of Fidel Castro at the UN General Assembly in New York.
There was no picture of the moment and the White House initially denied it had occurred.
Havana and Washington have not had diplomatic relations since 1961, two years after Fidel Castro came to power in the Cuban revolution.
Since Obama took office tensions have eased, with both countries reaching a series of agreements seen as confidence building measures including cooperation on air and maritime rescue, migratory issues.
In 2011 Obama eased restrictions on visas, remittances and travel.
The move was designed to expand religious and educational travel, allow any airport to offer charter flights to the country and restore cultural initiatives suspended by the previous Bush administration.
Talks are underway to resume a direct postal service between the two countries.