There are 33 million people living with HIV in the world
There is no evidence that a £6 billion UK drive to tackle the Aids epidemic abroad will meet its early targets, according to a committee of MPs.
The International Development Committee said the strategy was "strong on rhetoric" but lacked vital details.
The government has pledged the cash over seven years and wants to see universal access to HIV prevention and treatment by 2010.
It said it will publish more detailed plans on Monday - World Aids Day.
The MPs have called for a full breakdown of where the money was to be spent.
The strategy was published in June by the Department for International Development (DfID), but MPs said they were still waiting for more information - and evidence that targets would be met.
There are 33 million people living with HIV/Aids in the world, with nearly 6,000 dying each day, and an estimated 7,000 new infections every day.
Much of the fresh effort will be targeted at the epicentre of HIV infection in the world - sub-Saharan Africa.
However, while welcoming this, the committee said it was concerned that important groups, such as those at risk of infection through rape, or vulnerable "marginalised groups" such as prostitutes, drug users and homosexual men, might be overlooked.
The committee's chairman, Liberal Democrat Malcolm Bruce said: "We were shocked to learn that young girls in some countries in Africa are more likely to be raped than to learn how to read and write - sexual violence is a major factor in the spread of HIV.
"We need to know what programmes DfID intends to support to tackle gender-based violence.
"It is not yet clear to us whether the £6 billion is new money or simply a redirection of existing commitments - we have asked the department for a full breakdown of where this sum will come from and how it will be spent on the ground."
He said that he had seen no evidence yet that the project was on track to meet the 2010 target.
DfID said it was preparing to launch, on World Aids Day itself, a "Monitoring and Evaluation Framework" which should contain more information about how the money is spent.
International Development minister Ivan Lewis said the UK was "widely acknowledged" as a pioneer in the fight against HIV and Aids.
He said: "Between now and 2015 the UK will invest £6 billion to ensure countries with the least developed health systems can fight and win the battle against Aids."
The International HIV/AIDS Alliance welcomed the committee report, but Anton Kerr, its senior policy adviser, said that the government's existing efforts to tackle HIV were helping to "deliver results", including a 40-fold increase in access to antiretroviral treatments in Africa.
"However, the IDC report does raise questions about how DfID will support the increase to universal access in HIV services for those most vulnerable to HIV - such as men who have sex with men, injecting drug users, vulnerable women and children.
"We look forward to working with DFID to build on the significant achievements that have been made to date. Too much is at stake if we do not build on our achievements and scale up the global response."
AIDS charity the Terrence Higgins Trust was also supportive of the government's work in this area, but suggested there was no harm in MPs seeking greater accountability.
Lisa Power, head of policy for the charity, told BBC Radio's 5 Live: "I think it's important to remember that in terms of global support around HIV, the UK has been a shining light.
"DFID (the Department for International Development) has done a brilliant job so far but they are talking about changes in strategy now and I think it is reasonable that the committee asks them to justify those changes."