Barack Obama, Raul Castro shake hands at Mandela memorial

U.S. President Barack Obama shook hands with Cuban President Raul Castro today at a memorial servicefor former South African president Nelson Mandela an almost unprecedented moment between two deeply opposed neighbours.

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The handshake came during a ceremony focused on Mandela's legacy of reconciliation.

The U.S. and Castro have been enemies since the Cuban revolution led by Castro's olderbrother, Fidel, in 1959.AfterU.S.businesses in Cuba werenationalizedwithout compensation, the U.S. broke off diplomatic relations and imposeda trade embargo. Cuba's new regime then allied itself with the Soviet Union and began taking aid from the far side of the iron curtain.

Obama bounded up a set of stairs and was greeting a line of world leaders and heads of state attending the memorial in Johannesburg just before he spoke to the gathered thousands at FNB Stadium in Soweto.

A White House aide later described the handshake with Castro as unplanned and said the U.S. still has grave concerns about the human rights situation in Cuba, Reuters reported.

"Nothing was planned in terms of the president's role other than his remarks," deputy national security adviser Ben Rhodes told reporterstravelingwith Obama.

"He really didn't do more than exchange greetings with those leaders on his way to speak. It wasn't a substantive discussion."

The handshake drew criticism from some Republican politiciansin Washington, D.C.

At a congressional hearing,Republican Ileana Ros-Lehtinen of Florida chided Secretary of State John Kerry about the gesture.

"Sometimes a handshake is just a handshake, but when the leader of the free world shakes the bloody hand of a ruthless dictator like Raul Castro, it becomes a propaganda coup for the tyrant," Ros-Lehtinen said."Could you please tell the Cuban people living under that repressive regime that, a handshake notwithstanding, the U.S. policy toward the cruel and sadistic Cuban dictatorship has not weakened?"

The U.S. and Cuba have taken small steps toward peace in recent years, raising hopes they could be on the verge of a breakthrough in relations.

Still, skeptics caution that the two countries have shown signs of a thaw in the past, only to fall back into old recriminations.

Canada, for the most part, has maintained warm relations with Cuba since the days of former prime minister Pierre Trudeau's visits to the country in the1970s. He and Fidel Castro, who fell ill in recent years, remained on good terms.

Shark-infested straits

Obamaalso shook hands with Brazilian President Dilma Rousseff, who followed him onto the podium during the Mandela memorial, and has clashed with Obama over alleged National Security Agency spying.

Cuba has been a hot button in U.S. politics for decades. The southern coastal state of Florida is home to thousands of Cuban refugees and their descendants.

The shark-infested Florida Straits, known fordifficultcurrents and sudden squalls, separatethe southeast coast ofFlorida from Cuba. Many would-be Cuban immigrants to the U.S. have diedtrying to cross the straits as they flee their Communist-ruledhomeland.

CBC's PeterMansbridgenoted that Obama spoke of the Mandelalegacy even asleaders such as Castro, Zimbabwe PresidentRobert Mugabeand South African President JacobZumasat nearby all of them criticized in recent years for acts of oppression against some of their own people.

Still resisting reforms

"We, too, must act on behalf of justice," Obama said. "We, too, must act on behalf of peace.

"There are too many people who happily embrace Madibas[Mandela's]legacy of racial reconciliation, but passionately resist even modest reforms that would challenge chronic poverty and growing inequality.

"There are too many leaders who claim solidarity with Madibas struggle for freedom, but do not tolerate dissent from their own people. And there are too many of us on the sidelines, comfortable in complacency or cynicism when our voices must be heard."

The BBC reported in 2000 that then U.S. President Bill Clintonhad shaken hands with the Cuban president at the time, Fidel Castro, at a UN summit in New York.The White House originally denied that the handshake had taken place, but later admitted it had occurred, the BBC said.