US President Barack Obama saluted anti-apartheid icon Nelson Mandela on his 93rd birthday on Monday, saying he set the standard for service delivery by civil servants world-wide.

"Michelle, and my daughters, Sasha and Malia, recently met Madiba during an official visit to South Africa that focused on service, youth leadership, education and healthy living. Their time with Madiba was the most moving part of their trip," Obama said in a statement issued by the US diplomatic mission to South Africa.

"Mandela's legacy exemplifies wisdom, strength and grace, and on the anniversary of his birth we salute the example of his life."

Obama said Mandela, who led the African National Congress struggle against apartheid and became South Africa's first democratically elected president, continued to be a "beacon for the global community".

"On behalf of the people of the United States, we congratulate Nelson Mandela, and honour his vision for a better world...

"A man who devoted 67 years of his life to public service, Madiba sets the standard for service world-wide, whether we are students, shopkeepers or farmers, cabinet ministers or presidents. He calls on us to serve our fellow human beings, and better our communities."

Obama said the United States was honoured to join 192 United Nations member states in 2009 to declare July 18 Nelson Mandela International Day, in recognition of his contribution to peace and freedom.