PRETORIA, South Africa - Nelson Mandela called for unity in South Africa's governing party at a rally marking his 90th birthday Saturday, saying the African National Congress was responsible for making him the person he is today.

The Nobel Peace Prize winner urged tens of thousands at the rally to focus their celebrations not on him but rather the party that helped bring about the end of white racist rule in South Africa.

"Do not celebrate an individual,'' he said. "Celebrate the achievements and reaffirm the values of a great organization.''

Mandela was flanked by his successor to the South African presidency, Thabo Mbeki, and ANC president Jacob Zuma. The two fought bitterly over the party leadership last year and the battle seriously damaged the reputation of the party as it heads for general elections next year.

"Let no individual, section, faction or group ever regard itself as greater than the organization,'' Mandela said. "Our nation comes from a history of deep division and strife; let us never, through our deeds or words, take our people back down that road.''

Mandela was imprisoned for nearly three decades for his fight against apartheid. He was released in 1990 and was elected president in 1994. He completed his term in 1999 and did not run again, but has taken a leading role in the fight against poverty, illiteracy and AIDS in Africa.

On Saturday, Mandela beamed and clapped along as a group of small children sang a song for him. Behind him stood his former wife, Winnie Madikizela-Mandela, and his wife of 10 years, Graca Machel, arm-in-arm, swaying to the music.

Later Mandela cut a huge cake while the party leadership and his family toasted him. Balloons in the green, gold and black colours of the ANC were released into the sky.

South Africa has been celebrating Mandela's July 18 birthday since the start of the year including museum exhibitions, reunions of anti-apartheid veterans, and the launch of special coins and stamps.

After formal events in London and at his rural homestead, Saturday was a chance for South Africans to wish him happy birthday.

People poured out of buses singing and wearing white T-shirts with Mandela's face emblazoned on them.

Mary Skhosana, 19, came from Muldersdrift, a small town west of Johannesburg, to wish Mandela happy birthday.

"To me he has been a father, a hero,'' she said.