QUNU, July 19, 2008 (AFP) - Democratic presidential contender Barack Obama on Saturday praised Nelson Mandela's courage and conviction in a video tribute made to mark the South African hero's 90th birthday.

'When I visited South Africa a few years ago, I had a chance to go to Robben Island and stand in your cell, and I reflected on your courage, your foresight and conviction, and on your fundamental belief that we do not have to accept the world as it is; that we can remake the world as it should be,' he said.

The US senator's video message was run at the Mandela Museum in Mandela's home village of Qunu, where a select gathering of family and friends were helping their former president, the anti-apartheid legend, celebrate.

'This is the story of 90 remarkable years that we celebrate today,' said Obama.

'But celebrations and simple words of admiration are not enough,' he added.

'They're not enough to honour a man who's brought hope to a world often filled with despair; who's brought so much love to a world so filled with hate and who's shown us how much we can achieve when we have the courage to be our better selves.'

'No, the way to truly honour you, Nelson Mandela, is to act each and every day in our own lives to do our part for our fellow human beings and to live up to the example you continue to set each and every day.'

Obama is aiming to make history by becoming the United States' first black president.

His tribute was registered as an exhibit at the new exhibition at the museum dedicated to the life of Mandela and the black American civil rights campaigner Rosa Parks.

Parks, who made history when in 1955 she refused to give up a seat reserved for whites on a bus in Alabama, in the southern United States, became a close friend of Mandela after his release from prison in 1990. Parks died in 2005.