Mr Obama and his family visited Mr Mandela's jail cell and the quarry where Mr Mandela was forced to labour
US President Barack Obama has toured Robben Island - the jail in which Nelson Mandela was kept for 18 years.
He said he and his family were "deeply humbled" to visit the
prison once inhabited by Mr Mandela - who remains critically ill in
hospital.
Mr Obama will go on to give a speech at the University of Cape Town and launch a multi-billion-dollar electricity initiative.
The US leader did not visit Mr Mandela, but met the Mandela family in private.
Security is likely to have been strengthened during this
final Cape Town leg of his time in South Africa, says the BBC's Karen
Allen who is there, following clashes on Saturday between riot police
and anti-Obama protesters in Soweto.
At the scene
Joseph Winter
BBC News, Pretoria
More than three weeks after Nelson Mandela was taken to
Medi-Clinic Heart Hospital in Pretoria, there is still a steady stream
of well-wishers, leaving flowers and tributes to add to the huge
collection outside the gates.
On Sunday morning, two church groups were singing hymns,
while veterans from Umkhonto we Sizwe (MK), the ANC's armed wing set up
by Mr Mandela, arrived with a portrait of their founder wearing a
military uniform.
The tributes come from around the world - Pakistan, Mexico
and France - as well as several African countries. And in a testimony to
Mr Mandela's dream of creating a rainbow nation, all of South Africa's
racial groups were represented.
As she left a bunch of white chrysanthemums, Raksha Daya said
that like many South Africans, she connects with the former president
on a deeply personal level, like a grandfather. "It's a sense of love."
'Heroes'
Mr Obama and the first family visited
Mr Mandela's bleak cell as well as the lime quarry - overlooked by a
concrete watchtower - where anti-apartheid fighters including Mr Mandela
were forced to undertake hours of back-breaking labour.
Mr Mandela was at the prison for 18 years and his long
history of lung problems can be traced to the tuberculosis he contracted
there - which he attributed to the dampness of his cell.
Later, Mr Obama wrote in the guest book in the prison
courtyard: "On behalf of our family, we're deeply humbled to stand where
men of such courage faced down injustice and refused to yield.
"The world is grateful for the heroes of Robben Island, who
remind us that no shackles or cells can match the strength of the human
spirit."
Mr Obama will also visit a community project before delivering a keynote address at the University of Cape Town.
It is the same venue where 47 years ago, US Senator Robert
Kennedy gave his famed "ripple of hope" speech, which gave inspiration
to those fighting the racially divisive policies of apartheid rule and
linked their struggle with that of the US civil rights movement.
Mr Obama is expected to pay tribute to South Africa's
achievements over the past two decades but is expected to stress that
more needs to be done to tackle poverty and disease, and strengthen
democracy across the continent.
Nelson Mandela: Key dates
- 1918 Born in the Eastern Cape
- 1944 Joins African National Congress
- 1956 Charged with high treason, but charges dropped
- 1962 Arrested, convicted of sabotage, sentenced to five years in prison
- 1964 Charged again, sentenced to life
- 1990 Freed from prison
- 1993 Wins Nobel Peace Prize
- 1994 Elected first black president
- 1999 Steps down as leader
He is also due to announce a $7bn
(£4.6bn) five-year initiative to double access to electricity in
sub-Saharan Africa, in partnership with African countries and the
private sector.
Beacon
Mr Obama has been faulted for lacking a grand programme and
many Africans have been disappointed at what they see as his lack of
engagement with the continent, despite his African ancestry.
In Pretoria on Saturday, Mr Obama said Mr Mandela's example
of "the power of principle, of people standing up for what's right
continues to shine as a beacon".
Later, riot police fired rubber bullets and stun grenades at
scores of protesters in Soweto, once a flashpoint in the anti-apartheid
struggle.
At least one person was injured and one arrested.
"People died in Libya, people are still dying in Syria... in
Afghanistan, in Pakistan, drones are still killing people. So that's why
we are calling him a Hitler. He's a killer,'' Ramasimong Tsokolibane,
54, was quoted as saying by the Associated Press news agency.
Mr Obama arrived in South Africa from Senegal on Friday evening. On Monday, he will continue his African tour in Tanzania.
Family row
Mr Mandela's family heir, Mandla, has said he will oppose a
court action brought by the rest of the family, seeking to exhume the
bodies of his father, Makgatho, two of Nelson Mandela's daughters and
two other relatives.
The rest of the family want the remains to be reburied in
Qunu, where the former South African president wants to be laid to rest,
while Mandla, an ANC MP, wants them to stay in the nearby village of
Mvezo, Nelson Mandela's birthplace, where he is building a museum
dedicated to his grandfather.
This is an extremely important matter for the Mandela family,
especially while he remains critically ill in hospital - it is one of
the reasons why they held a family meeting last week.
South Africa's Sunday Times newspaper quotes local chiefs in
the area as saying that Madiba, as Nelson Mandela is known in the
country, will not be at peace until this issue is resolved.
On Friday, a court granted an interim action saying the
bodies could be exhumed and reburied but Mandla Mandela says he was not
aware of the case until it was reported in the media and he is now
opposing it.