American Secretary of State Colin Powell has said the US is making a greater contribution to fighting HIV/Aids than any other country.
Mr Powell said sexual abstinence could help stop Aids
Mr Powell told the BBC that the Bush administration was not backtracking on its commitment to spend $15bn on Aids over the next five years.
He said Aids was a national security issue, because it tore countries apart.
And he defended plans to spend one-third of the money on programmes promoting sexual abstinence.
Mr Powell's comments, in an exclusive BBC interview, came amid concern that President George W Bush has asked Congress to appropriate just $2.1bn for fighting Aids in 2004.
The BBC's Michael Buchanan in Washington says most people had assumed the president would spend $3bn a year on the anti-Aids initiative.
But Mr Powell said the US was committed to spending every cent of the $15bn.
He said: "We expect Congress to appropriate it and we will spend it, because there's a desperate need out there for it."
The US secretary of state also rejected suggestions that it was unrealistic to allocate one-third of the money to programmes that promoted abstinence from sex.
He said: "Abstinence works, we know it works. If you're not actually transmitting the disease through sexual conduct, the disease will not be transmitted."
However, Mr Powell stressed that sexual abstinence was being promoted as part of a comprehensive approach to HIV and Aids that also included education, promotion of safe sex and condoms, treatment programmes and research into a cure.
"Abstinence is a good thing to teach young people before they're ready for the responsibilities of sexual activity," he said.
Mr Powell said the HIV/Aids epidemic was threatening the viability of some countries: "It leaves families totally torn apart, villages torn apart, and in due course, countries torn apart."
Aids activists expressed concern at the decision to ask for only $2.1bn to fight the disease next year, saying they feared the programme could fall foul of budget cuts as the US deficit rose to new heights.
One Democrat congresswoman, Nita Lowey, said: "I think it's truly unfortunate that the President talked the talk but wasn't willing to walk the walk."
Sandra Thurman, of the International Aids Trust, said: "I do have fears that among competing priorities in the United States, with a growing deficit, that there is a huge challenge getting enough money to fund these programmes."
She added: "If we're going to increase our debt, the thing they can't stop funding are the things that matter most, and that's providing care and services to people at risk for HIV and living with Aids."