South Africa's iconic former leader Nelson Mandela has lapsed into critical condition after spending more than two weeks in a Pretoria hospital to treat a lung infection, according to a statement from the president's office.

President Jacob Zuma and deputy president of the ruling African National Congress, Cyril Ramaphosa, visited Mr. Mandela at the hospital Sunday evening. The medical team treating Mr. Mandela told the pair of visitors the condition of the 94-year-old former president had 'become critical over the past 24 hours,' according to the president's office.

'The doctors are doing everything possible to get his condition to improve and are ensuring that Madiba is well-looked after and is comfortable,' Mr. Zuma said referring to Mr. Mandela by his clan name.

For the past two weeks, the presidency has described Mr. Mandela's condition as 'serious but stable.' On Sunday, Mr. Zuma's spokesman Mac Maharaj described a sharp deterioration of Mr. Mandela's condition but wouldn't provide details, citing the ailing leader's privacy. 'His condition is clearly worse than serious, and clearly he's receiving intensive care treatment,' Mr. Maharaj said. 'What form that takes I'm not in a position to go into.'

Mr. Mandela was admitted on June 8 for treatment of a lung infection, one in a long series of respiratory ailments he has battled since contracting tuberculosis during his 27 years in prison for opposing South Africa's former white-minority apartheid regime.

This is his fourth hospitalization since December. The visits have caused ripples of anxiety in South Africa, where Mr. Mandela has long been a unifying figure in a racially-polarized nation.