PRETORIA: A gravely ill Nelson Mandela showed tentative signs of improvement Thursday as South Africa-bound US President Barack Obama led a chorus of support for the “hero for the world”.

South African President Jacob Zuma, who had abruptly cancelled a trip abroad to be near the 94-year-old anti-apartheid icon, reported he “remains critical but is now stable”.

“He is much better today,” Zuma said in a statement without giving more details. “The medical team continues to do a sterling job. We must pray for Tata's (father's) health and wish him well.”Grandson Mandla Mandela said the Nobel Peace laureate's fate “lies with God and our ancestors”.

“Every improvement in my grandfather's health is cause for celebration.””He is a personal hero,” said US President Barack Obama, who is due to fly into Pretoria later Friday.

“I think he is a hero for the world, and if and when he passes from this place, one thing I think we all know is that his legacy is one that will linger on throughout the ages.”Obama recalled how Mandela had inspired him to take up political activity, when he campaigned for the anti-apartheid movement as a student in the late 1970s.

He was speaking on Thursday from Senegal, the first leg of an African tour.

As Mandela fights for his life after three weeks of intensive care, South Africans remain braced for the worst. A large number of family members gathered Thursday at the hospital where he was admitted on June 8 with a recurring lung infection.

“I won't lie. It doesn't look good,” oldest daughter Makaziwe Mandela said. But “if we speak to him he responds and tries to open his eyes -- he's still there.

“Anything is imminent, but I want to emphasise again that it is only God who knows when the time to go is,” she told local radio.

Clan elder Napilisi Mandela told AFP late on Wednesday that the former South African president was “using machines to breathe”.

A group of family members on Thursday walked to the wall of messages and flowers where emotional crowds have been holding vigils, offering their prayers for one of the greatest figures of the 20th century.

Supporters, including members of Mandela's African National Congress, sang songs in tribute to the man who led the transition from centuries of white minority rule to landmark multiracial elections.

“There is no sadness here. There is celebration. He is a giant,” said Nomhlahla Donry, 57, whose husband served time with the revered leader.