JOHANNESBURG (REUTERS) - Former South African President and anti-apartheid hero Nelson Mandela was in a "serious but stable" condition after being taken to hospital early on Saturday with a recurrence of a lung infection, the government said.

The 94-year-old, who became the first black leader of Africa's biggest economy in 1994 after historic all-race elections, has been in hospital three times since December. He has been battling the infection for several days, a statement said.

"This morning at about 1:30 a.m. (7:30 am Singapore time) his condition deteriorated and he was transferred to a Pretoria hospital. He remains in a serious but stable condition," the government said.

The wording of the government statement, in particular the use of the word "serious", is clear cause for concern to South Africa's 53 million people, for whom Mr Mandela remains a potent
symbol of the struggle against decades of white-minority rule.

However, presidential spokesman Mac Maharaj told local television that "doctors have assured us he is comfortable".

The Nobel Peace Prize laureate stepped down as president in 1999 after one term in office and has been removed from politics for a decade.

His last appearance in public was at the final of the soccer World Cup in Johannesburg in 2010. He appeared in a brief television clip aired by state television in April during a visit to his home by President Jacob Zuma.

The ruling African National Congress (ANC) assured the public Mandela was "in good shape", although the footage showed a thin and frail old man sitting expressionless in an armchair with his head propped against a pillow.

Since his withdrawal from public life, he has divided his time between his plush Johannesburg home and Qunu, the village in the impoverished Eastern Cape where he was born and spent his early years.

Mr Mandela spent nearly three weeks in hospital in December with a lung infection and after surgery to remove gallstones. That was his longest stay in hospital since his release from
prison in 1990 after serving almost three decades behind bars or on the Robben Island prison camp for conspiring to overthrow the apartheid government.

His history of lung problems dates back to his years on Robben Island, where he contracted tuberculosis.

Although he remains deeply revered, Mr Mandela is not without his detractors both at home and in the rest of Africa. Some of them feel he made too many concessions to the white minority in the post-apartheid settlement.

Despite more than 10 years of policies aimed at redressing the balance, whites still control much of the economy and an average white household earns six times more than a black one.

"Mandela has gone a bit too far in doing good to the non-black communities, really in some cases at the expense of (blacks)," Zimbabwean President Robert Mugabe, 89, said in a
documentary aired on South African television this month.

"That's being too saintly, too good, too much of a saint."