PRETORIA, South Africa -- U.S. President Barack Obama and First Lady Michelle Obama will meet on Saturday with relatives of anti-apartheid hero Nelson Mandela, but they will not visit the hospital where the former South African president is critically ill, the White House said. Obama is in South Africa on the second stop of a three-nation Africa tour. His visit had triggered intense speculation that the United States' first African-American president might visit 94-year-old Mandela in the Pretoria hospital where he has spent three weeks being treated for a lung infection.