President Barack Obama shakes Raul Castro's hand at Mandela memorial service

The US president, Barack Obama, shook hands with his Cuban opposite number, Raul Castro, at the memorial service for Nelson Mandela.

The handshake between the two historic enemies came as they attended a ceremony in Johannesburg to celebrate the late South African leader's ability to foster reconciliation. The gesture - which comes despite half a century of hostilities - came as Mr Obama made his way to a podium to deliver a speech. It is only the second time ever that a US president has shaken the hands of a Cuban Communist leader. President Bill Clinton was the first to do so in 2000 after a lunch during a United Nations summit in New York, when he shook hands with Mr Castro's brother, Fidel.On that occasion, the White House initially denied the handshake had taken place but later backtracked, saying it had been instigated by Mr Castro, who had approached Mr Clinton. Unlike the latest occasion, however, the exchange was not photographed.Under diplomatic protocols established years ago, Cuba's president and Washington's representatives are rarely invited to the same events. If they do, the meeting is choreographed so that they are not likely to meet face to face. Given the legacy of Cold War hostility between the USA and Cuba - which brought America to the brink of nuclear war during the Cuban missile crisis in 1962 - any handshake by a US president risks a backlash from more hawkish elements in US public opinion. A similar gesture was widely expected during America's recent talks with Iran over its nuclear programme, which saw American and Iranian presidents talk direct on the phone for the first time in 30 years. But in the end, the expected handshake never came off - allegedly because of fears among aides to the Iranian president, Hassan Rouhani, that it would lead to criticism among hardliners in his own camp. In today's ceremony in South Africa, Mr Obama also shook the hand of Robert Mugabe, the president of Zimbabwe, and of Dilma Rousseff, the president of Brazil, a noted critic of the US government.