U.S. President Barack Obama paid tribute to anti-apartheid hero Nelson Mandela as he flew to South Africa to meet his counterpart Jacob Zuma on Saturday.

President Obama is on a three-nation African trip.Obama is unlikely to meet the world's peace icon as the 94-year-old is in a critical condition, battling for his life in a hospital in Pretoria since June 8. He described the anti-apartheid leader as a "hero for the world."

Mandela's ex-wife, Winnie Madikizela-Mandela also told reporters Friday that it would not be right for the U.S. president to visit the ailing Mandela while he was in a critical condition.

"I'm not a doctor but I can say that from what he was a few days ago there is great improvement, but clinically he is still unwell," said Madikizela-Mandela according to the BBC News.

Earlier, before flying to South Africa, Obama said "I don't need a photo op," adding "The last thing I want to do is to be in any way obtrusive at a time when the family is concerned with Nelson Mandela's condition."

"I think the main message we'll want to deliver is not directly to him, but to his family - is simply profound gratitude for his leadership all these years, and that the thoughts and prayers of the American people are with him, his family and his country," said Barack Obama.

Under the umbrella of the South African Communist Party and the Congress of South African Trade Unions, several dozens of people were seen protesting in front of the U.S. embassy in Pretoria hours before Obama's visit, calling for an end to U.S. "warmongering."  

However, the South African government called Obama's visit to the country as "historical."

After bilateral talks, the two leaders are scheduled to give a joint press conference and later President Zuma will host a dinner.

Noting that China, Brazil, India and other countries were increasingly showing interest in Africa, the U.S. president said Washington could not risk being left out.

"They recognize that China's primary interest is being able to obtain access for natural resources in Africa to feed the manufacturers in export-driven policies of the Chinese economy," said the U.S. president speaking to a group of farmers and entrepreneurs in Senegal.

"Oftentimes that leaves Africa as simply an exporter of raw goods," he said. According to him, the U.S. approach to development is applauded by the African leaders.