Nelson Mandela
Nelson Mandela has been admitted to hospital four times in three years due to health problems.

Former South African President Nelson Mandela has been readmitted to hospital after suffering from another bout of the lung infection he originally contracted 30 years ago.

No details about his condition or the hospital which is treating him have been released.

President Jacob Zuma issued a statement wishing Mandela speedy recovery: "We appeal to the people of South Africa and the world to pray for our beloved Madiba [Mandela's clan name] and his family and to keep them in their thoughts.

"We have full confidence in the medical team and know that they will do everything possible to ensure recovery."

This is the fourth time in three years that the 94-year-old anti-apartheid icon has been admitted to hospital for the recurring lung problem.

In January 2011, he was admitted to hospital for two and a half days with a respiratory infection, and was back in hospital the following December with a similar problem. He underwent endoscopic surgery to have his gallstones removed a week later the same month, and also spent a night in a Pretoria hospital earlier this month following a routine health check-up.

Mandela first contracted the lung infection while serving time on Robben Island as a political prisoner during the 1980s.