Access to antiretroviral therapy remains limited
Millions of people with HIV/Aids in poor countries still do not have access to potentially life-saving drugs.
A major report found just 31% of people in need of treatment in low and middle-income countries had access to antiretroviral therapy (ART) in 2007.
The report, by the World Health Organization (WHO), UNAids and Unicef, said an extra 950,000 people in these countries received the drugs last year.
The agencies admit they are two years behind their access target.
WHO and UNAids aimed to have three million people on ART by the end of 2005.
But by the end of 2007, the total number on treatment had still not quite reached that figure, leaving an estimated 6.7 million people unable to access potentially life-saving drugs.
The report says that by the end of 2007 an estimated 33.2 million people worldwide were living with HIV, with 2.5 million people newly infected during the year.
It found that there had been a significant improvement in the availability of HIV testing and counselling services.
Unaware of status
However, the majority of people living with HIV/Aids remain unaware of their status - surveys carried out in 12 countries with a high level of infection found that on average just 20% of people were aware that they were carrying the virus.
The report blames the failure to achieve more widespread access to drugs on weak healthcare systems in badly affected countries, coupled with a lack of trained staff and sustainable, long-term financing.
A "brain drain" of skilled healthcare workers to other occupations and other countries is a significant factor in the hardest-hit regions.
The report also says that countries require monitoring systems to track the progress and impact of HIV programmes.
Kevin De Cock, WHO HIV/Aids director, said: "The answer to the HIV epidemic is preventing new infections.
"An additional 1 million people came on to therapy but another 2.5 million became newly infected with HIV, so we have to do better with prevention."
The report says there have been areas where significant progress has been made, including improved access to treatment for pregnant women to stop them passing the virus on to their child. In total, 500,000 such women received antiretrovirals in 2007 - up from 350,000 in the previous year.
Male circumcision - which can reduce the risk of passing on HIV during sex - is also now more effectively promoted in heavily affected regions of sub-Saharan Africa.
The UK's Department for International Development has announced that it will spend £6bn ($12bn) on improving health systems and services in poor countries up to 2015, with HIV at the top of the agenda.
Douglas Alexander, Secretary of State for International Development, said: "This will mean more and better equipped doctors and nurses, improved facilities and more people being able to access the HIV prevention, treatment, care and support that they need."
While ART is a very effective treatment, there remains no cure for HIV.