President George W Bush has asked the US Congress to set aside $30bn (£15bn) over five years for the global fight against HIV/Aids.
Sub-Saharan Africa still sees the most cases of HIV/Aids
He said the sum would double the current US commitment and provide treatment for 2.5 million people.
Mr Bush said the funding would also be aimed at preventing more than 12 million new infections.
The president said his wife Laura would visit Africa next month as part of the US campaign against Aids.
"When I took office, an HIV diagnosis in Africa's poorest communities was usually a death sentence," Mr Bush said.
"Once again, the generosity of the American people is one of the great untold stories of our time."
In 2003, the US Government approved a $15bn package over five years to fight the spread of Aids.
The US Congress stipulated that a proportion of those funds must be spent on encouraging abstinence-until-marriage programmes.
United Nations agencies say about 40 million people worldwide are infected with Aids or HIV.
Almost three-quarters of deaths from Aids last year occurred in sub-Saharan Africa, and two-thirds of those living with HIV are found there.
The number living with the virus has increased everywhere, with the most striking increases in East Asia and Central Asia/Eastern Europe.
On Wednesday the World Health Organization urged affected countries to carry out HIV tests on everyone attending health centres unless they "opt out".
It said 200 million people could benefit from the policy.
Currently 80% of people infected with HIV in areas such as sub-Saharan Africa do not know they have it.