With his voice sometimes cracking with emotion, Irish rock star Bono joined US Treasury Secretary Paul O'Neill on a visit to a South African hospital for mothers infected with HIV.

I'm actually speechless

Bono

The Irish star came face to face with Africa's Aids tragedy at the 2,888-bed Chris Hani Baragwanath hospital in Soweto, which is said to be the world's biggest.

Bono and Mr O'Neill are on a 10-day four-nation tour of the continent aimed at improving the impact of development aid.

Although many of the HIV positive women had never heard of the two men, they appeared visibly touched that such clearly important people were interested in their plight.

The women are among the 4.7 million people infected with HIV/Aids in South Africa.

Zulu choir

"This is an amazing place, amazing people," Bono said.

"This is very, very hard for an Irish rock star to admit.

"I'm actually speechless."

A female choir singing a local Zulu song welcomed Mr O'Neill, dressed in his business-like dark tie, dark suit and white shirt, and Bono, hands in pocket, unshaven, gold earrings and ever-present sunglasses.

Bono says Africa's Aids epidemic should be tackled now

Later Bono, the lead singer of the band U2, gave an impromptu performance at a shanty town in Soweto, accompanied by clapping and a man playing a traditional drum.

The tour is the result of a meeting a year ago when the two men met in Mr O'Neill's office in Washington.

Earlier on Friday, Mr O'Neill, the world's most powerful finance minister, and Bono, the advocate of debt relief to poor nations, toured the Ford FN motor plant in Pretoria, believed to be the biggest auto assembly plant in sub-Saharan Africa with a workforce of 3,500 workers.

The Irish star noted that the plant was considered to have the most exemplary HIV/Aids policy and was full of praise:

"You can't have the benefits of a global market without some kind of responsibilities."

Asked about South African President Thabo Mbeki's controversial stance on Aids, questioning the link between HIV and Aids, Bono told reporters:

"He (Mbeki) is turning. I think we've got to give him a bit of room."

Diplomatic hiccup

On Thursday Mr O'Neill and Bono met Mr Mbeki and Finance Minister Trevor Manuel.

But cracks began to emerge on what has so far been a sterling roadshow between the two unlikely duo when Bono told reporters the Mr Mbeki had raised the issue of recently enacted US farm subsidies as a stumbling block to promoting free trade between the US and Africa.

US Treasury officials travelling with Mr O'Neill later denied Mr Mbeki had raised the issue of farm subsidies as Bono had said.

But most of the time the two men seemed to be gently sparring about each other's role in fostering aid for Africa, particularly in the fight against Aids.

"The secretary will be able to send one message back to the president.

"This is an emergency what we have seen today."

Mr O'Neill responded: "We, the world, have got to deal with this problem. ... This is doable."

After South Africa, Bono and Mr O'Neill are to visit Uganda and then Ethiopia.