We have the power to help

President Bush

Referring to the spread of Aids in Africa, Mr Bush said: "In a part of the world where so many have suffered from war and want and famine, these latest tribulations are the cruellest of fates. We have the power to help."

But Aids activists have criticised the American donation - which will also be used to help fight malaria and tuberculosis - as paltry.

War chest

President Bush said the fund would seek to form "partnerships across borders and across public and private sectors".

Private corporations and individuals would also be tapped for funds, along with international foundations, non-government organisations and faith-based groups.

It sends a message to other wealthy nations that this UN trust fund, and the lives it could save, are not worth the investment

Health GAP Coalition

The announcement was made at a White House ceremony to greet the visiting Nigerian President, Olesegun Obasanjo.

Both he and UN Secretary General Kofi Annan thanked the US president for the contribution.

But Mr Annan, who proposed the creation of the fund last month, said a good deal more money was needed.

"As we declare global war on Aids, we will need a war chest to fight it. We need to mobilise an additional $7bn to $10bn a year to fight this disease well."

"To defeat this epidemic that haunts humanity, and to give hope to the millions infected with the virus, we need a response that matches the challenge," he said.

Aids activists slammed the $200m donation as shameful.

'Not enough'

The Health GAP Coalition released a statement saying: "It sends a message to other wealthy nations that this UN trust fund, and the lives it could save, are not worth the investment."

Africa is the continent hardest hit by Aids

"It's criminally small," said David Bryden of the Washington-based Global Aids Alliance, who wants the US to donate something closer to $2.5bn.

Last month, former US President Bill Clinton told an African Aids summit that he thought his country could easily afford to contribute $1.75bn.

Mr Bush said more US money would be made available when Washington had established where its support would be most effective.

Africa, where the vast majority of Aids sufferers cannot afford treatment, is expected to receive a large share of the funds.

Africa is home to more than 70% of the world's 36 million people infected with HIV.