"The global devastation of HIV-Aids staggers the imagination and shocks the conscience," he said at the White House.

He also called for other countries to help fight Aids in Africa where the disease is the continent's number one killer.

The money is aimed at funding programmes to cut mother-to-child transmission by 40% within five years or less in 12 African countries and the Caribbean.

But Aids campaigners have criticised the move saying the US is still not doing all it can to combat the disease.

Orphans crisis

South Africa, one of the initial recipients of the cash, was warned on Wednesday that more than five million children could be orphaned over the next 12 years because of the spread of Aids and HIV.

The US has ample resources to help fight global Aids, yet, sadly, the president still seems unprepared to show real leadership

Paul Zeitz of Global Aids Alliance,

Two million women infected with HIV become pregnant each year, most of of them in poor countries. Between one quarter and third transmit the disease to their babies - meaning 2,000 new Aids-infected babies are born every day.

Mr Bush stressed that the cash would be on top of �200m announced in May last year for the Global Fund to Fight Aids, Tuberculosis and Malaria.

His announcement is apparently part of a startegy to project a more compassionate image ahead of a summit in Canada next week.

A senior Bush advisor told the AP news agency that the aim was to soften criticism that the United States does not spend enough helping poor countries.

Prevention call

One of the main focuses of the Group of Eight meeting - leaders of the world's seven largest industrial powers and Russia - will be a new development plan for Africa.

But Aids groups said the cash was too narrowly tailored to help in the broader fight against Aids.

The South African Government says it does not have the funds for treatment

Paul Zeitz, executive director of the Global Aids Alliance, said: "The fact is that the US has ample resources to help fight global Aids, yet, sadly, the president still seems unprepared to show real leadership."

The alliance has urged the US administration to commit $2.5bn to combat the spread of Aids, treat patients, care for orphans and train doctors.

That would cover about one-third of the $7-$10bn a year UN Secretary-General Kofi Annan estimates is needed.

The Medical Research Council of South Africa (MRC) believes that unless there are major interventions or changes in sexual behaviour, up to 15% of children could lose one or both parents.

It said this would overwhelm formal as well as informal fostering systems.

The MRC called for treatment and prevention programmes aimed primarily at mothers, and said anti-retroviral (ARV) drugs should be made available to all patients.

But the recommendation will not be welcomed by the South African Government, which has refused to provide ARV treatment to all people who are HIV-positive. The authorities say they have neither the funds nor the infrastructure to do this.