JOHANNESBURG » Nelson Mandela, the former South African president and anti-apartheid leader, was admitted to a hospital today for a scheduled medical check-up and doctors say there is no cause for “alarm,” the president’s office said.

Presidential spokesman Mac Maharaj said 94-year-old Mandela went in the afternoon for tests “to manage existing conditions in line with his age” at a hospital in Pretoria, the capital.

“Doctors are conducting tests and have thus far indicated that there is no reason for any alarm,” Maharaj said in a statement. He appealed for the public to respect the privacy of Mandela and his family.

Mandela was hospitalized for nearly three weeks in December before going home on Dec. 26. At that time, he was treated for a lung infection and had a surgical procedure to remove gallstones.

The former president has become increasingly frail over the years. In January 2011, Mandela was admitted to a Johannesburg hospital for what officials initially described as tests but what turned out to be an acute respiratory infection. He was discharged days later. He also had surgery for an enlarged prostate gland in 1985.

Under South Africa’s white-minority apartheid regime, Mandela spent 27 years in prison, where he contracted tuberculosis, before being released in 1990. He later became the nation’s first democratically elected president in 1994 under the banner of the African National Congress. He served one five-year term before retiring.

The Nobel laureate last made a public appearance on a major stage when South Africa hosted the 2010 World Cup soccer tournament.

Although South Africa today struggles with poverty and inequality, Mandela is widely credited with helping to avert race-driven chaos as South Africa emerged from apartheid.