Former South African President Nelson Mandela was readmitted to the hospital with a recurrence of a lung infection.

JOHANNESBURG — Nelson Mandela, the anti-apartheid leader who became South Africa’s first black president, has been admitted to a hospital with a recurring lung infection, South Africa said today.

Mandela, 94, has become increasingly frail in recent years and has been hospitalized several times since last year, most recently earlier this month when he underwent what authorities said was a scheduled medical test. The Nobel laureate is a revered figure in South Africa, which has honored his legacy of reconciliation by naming buildings and other places after him and printing his image on national banknotes.

“I’m so sorry. I’m sad,” said Obed Mokwana, a Johannesburg resident. “I just try to pray all the time. He must come very strong again.”

The Nobel laureate was admitted to a hospital just before midnight Wednesday “due to the recurrence of his lung infection,” the office of President Jacob Zuma said in a statement.

“Doctors are attending to him, ensuring that he has the best possible expert medical treatment and comfort,” the statement said. It appealed “for understanding and privacy in order to allow space to the doctors to do their work.”

It did not identify the hospital. In December, Mandela spent three weeks in a hospital in the South African capital of Pretoria, where he was treated for a lung infection and had a procedure to remove gallstones.

Presidential spokesman Mac Maharaj acknowledged there was cause for worry, but said the medical specialists treating Mandela were very competent.