Nelson Mandela's health has deteriorated and he is in critical condition, the South African government said.

President Jacob Zuma has visited the 94-year-old anti-apartheid leader in hospital and was informed by the medical team that Mr Mandela's condition had become critical.

"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," Mr Zuma said in the statement, using Mr Mandela's clan name.

Mr Zuma met Graca Machel, Mr Mandela's wife, at the hospital in Pretoria and discussed the former leader's condition, according to the president's statement. Mr Zuma was accompanied by Cyril Ramaphosa, the deputy president of the country's ruling party, the African National Congress.

Mr Mandela was jailed for 27 years under white racist rule and released in 1990. He then played a leading role in steering the divided country from the apartheid era to democracy, becoming South Africa's first black president in all-race elections in 1994. He was taken to hospital on June 8 for what the government said was a recurring lung infection.

In the statement, Mr Zuma also discussed the government acknowledgement a day earlier that an ambulance carrying Mr Mandela to the Pretoria hospital two weeks ago had engine trouble, requiring the former president to be transferred to another ambulance for his journey. Pretoria, South Africa's capital, lies about 30 miles from Johannesburg, where Mr Mandela has been living.

"There were seven doctors in the convoy who were in full control of the situation throughout the period. He had expert medical care," Mr 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."

Mr Mandela, a Nobel Peace Prize laureate, is seen by many around the world as a symbol of reconciliation, and Mr Zuma appealed to South Africans and the international community to pray for the ailing ex-president, his family and the medical team attending to him.

The ruling party expressed concern about the deterioration in Mr Mandela's health.

"We welcome the work being done by the presidency to ensure that South Africans and people of the world are kept informed on the state of Madiba's health," the party said. "The African National Congress joins the presidency in calling upon all of us to keep president Mandela, his family and his medical team in our thoughts and prayers during this trying time."

In Washington, the White House's National Security Council said: "Our thoughts and prayers are with him, his family and the people of South Africa."

Prior to Mr Zuma's statement yesterday, reports from the government, former president Thabo Mbeki and a grandson of Mr Mandela had indicated that his health was improving, even though he has been in the hospital for treatment several times in recent months. In the days following his latest admission to hospital, Mr Zuma's office described Mr Mandela's condition as serious but stable. Family members have been seen making daily visits to the hospital where he is being treated.

Mandela, who has become increasingly frail in recent years, last made a public appearance at the 2010 World Cup tournament, hosted by South Africa. He did not deliver an address and was bundled against the cold in a stadium full of fans.

On April 29, state television broadcast footage of a visit by Mr Zuma and other leaders of the African National Congress to Mr Mandela's home. Mr Zuma said at the time that Mr Mandela was in good shape, but the footage - the first public images of Mr Mandela in nearly a year - showed him silent and unresponsive, even when Mr Zuma tried to hold his hand.

Between hospital stays in recent months, he has been staying at his home in the Johannesburg neighbourhood of Houghton, where he has received what the government described as "home-based high care" by a medical team. On April 6, he was discharged from a hospital after treatment for pneumonia, which included a procedure in which doctors drained fluid from his lung area.

Mr Mandela has been vulnerable to respiratory problems since contracting tuberculosis during his imprisonment under apartheid. Most of those years were spent on Robben Island, a forbidding outpost off the coast of Cape Town.