June 23, 2013 -- Nelson Mandela, the former president of South Africa, took a turn for the worse and was in critical condition today in his battle with a lung infection, according to a statement from the South African 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. He is in good hands," South African President Jacob Zuma said, using Mandela's tribal nickname.

Mandela had been listed in "serious but stable condition" for since he entered the hospital June 8.

The 94-year-old Nobel Peace prize winner's medical team informed the president's office that Mandela's condition become critical over the past 24 hours, according to the statement.

PHOTOS: Nelson Mandela Through the Years

Zuma reiterated today that Mandela's health was not compromised when the ambulance that was bringing him to the hospital in June 8 broke down.

"There were seven doctors in the convoy who were in full control of the situation throughout the period. He had expert medical care," Zuma said. "The fully equipped military ICU ambulance had a full complement of specialist medical staff including intensive care specialists and ICU nurses. The doctors also dismissed the media reports that Madiba suffered cardiac arrest. There is no truth at all in that report."

Mandela was forced to wait for a second ambulance after the first one broke down, the South African government admitted Saturday.

"When the ambulance experienced engine problems it was decided that it would be best to transfer to another military ambulance which itself was accompanied for the rest of the journey by a civilian ambulance," the president's office said Saturday.

Mandela was rushed to the hospital in the early morning hours of June 8, after his health deteriorated rapidly from a recurring lung infection.

News of Mandela's turn for the worse comes after a week in which there were several statement's that his health was improving.

Former South African president Thabo Mbeki suggested Saturday that Mandela was getting better.

After speaking to Mandela's doctors, Mbeki told a South African radio station, "Nelson Mandela is improving in terms of his health. I don't think anyone should entertain some sort of wrong notion that Nelson Mandela is about to die tomorrow. He's not going to."

Earlier this week, Mandela's daughter Zenani Mandela-Dlamini told a crowd of reporters outside Mediclinic Heart Hospital her father "is doing very well." President Jacob Zuma has also said publicly Mandela's health is "improving."

In April, Mandela spent 18 days in the hospital due to a lung infection and was treated for gall stones in December 2012.

Mandela served as the first black president of South Africa from 1994 to 1999.

In 1993, he received a Nobel Peace Prize for his work in ending apartheid through non-violent means.

ABC News' Brandi Hitt contributed to this report.