JOHANNESBURG — President Jacob Zuma said on Monday that Nelson Mandela remained in critical condition for a second day in a hospital in Pretoria where he is being treated for a lung infection.

“Doctors are doing everything possible to ensure his well-being and comfort,” Mr. Zuma said at a news conference in Johannesburg, but he gave few details about the condition of Mr. Mandela, who was hospitalized on June 8.

Mr. Zuma spoke as South Africans and admirers around the world awaited word on the condition of Mr. Mandela, the iconic leader who played a towering role in his country’s transition from white minority rule under the system of apartheid to multiracial democracy in 1994....