The ailing 94-year-old former President Nelson Mandela is in a worsening condition in hospital, having no impact on U.S. President Barrack Obama's visit, South Africa's President Jacob Zuma said on Monday. "Mandela remains in a critical condition in hospital, and doctors are doing everything possible to ensure his well-being and comfort," said Zuma in Johannesburg.

Mandela was admitted to hospital in Pretoria with the serious recurring lung infection on June 8.

On Sunday evening the Presidency said in a statement that Mandela's condition deteriorated over the past 24 hours.

Zuma stressed that Mandela's condition would not affect U.S. President Obama's visit to South Africa, saying "if there was such a visit, and somebody fell sick, I don't think we would stop the visit."

"Obama is coming," added he.

Obama is scheduled to pay his state visit to South Africa on Friday as part of his first major African three-nation trip.

It will be the first time for Obama to visit South Africa after assuming the office of U.S. president in January 2009.

On Friday, Deputy Minister of International Relations and Cooperation Ebrahim Ebrahim said Obama's visit will be important to the economy in South Africa.

During his stay in South Africa, Obama will visit Robben Island where Mandela was imprisoned for 18 years. On Friday the deputy U. S. national security advisor Ben Rhodes said Obama's visit to the island would be an important and powerful symbol of the president' s respect for Mandela.