Nelson Mandela has taken a turn for the worse and is now in critical condition at a South African hospital, officials said Sunday.

“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,” President Jacob Zuma said in a statement, referring to the 94-year-old former president by his nickname.

Zuma and African National Congress Deputy President Cyril Ramaphosa visited Mandela at the Pretoria hospital and were briefed on his condition by the medical team, the statement said. They asked the world to pray for the anti-apartheid icon and his family “during this difficult time.”

Dai Kurokawa / EPA

A portrait of former South African President Nelson Mandela rests against the wall as messages written by visitors are seen on the wall at Regina Mundi church in Soweto township, a flashpoint during the anti-apartheid struggle, in Johannesburg, South Africa, 23 June 2013.

Mandela, who has been in the hospital with a lung infection since June 8, had been in “serious but stable” condition but was downgraded in the last 24 hours, officials said.

In the statement, Zuma addressed reports that the ambulance that took Mandela to the hospital broke down on the way, saying that the delay did not compromise his health.

“There were seven doctors in the convoy who were in full control of the situation throughout the period. He had expert medical care,” his statement 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.”