Just 28% of poor people with HIV have access to the antiretroviral drugs that could save their lives, a study shows.
Antiretroviral drugs can keep HIV in check
The report is published by the World Health Organization, UNAids and Unicef.
It warned many obstacles remain to meeting the United Nations' target of universal access to HIV/Aids prevention and care programmes by 2010.
However, the report said "substantial, ongoing progress" had been made towards improving treatment and diagnosis of people with HIV.
Margaret Chan, WHO director general, said: "We need ambitious national programmes, much greater global mobilisation and increased accountability if we are going to succeed."
The report found that by the end of 2006, 2,015,000 people in low and middle-income countries were receiving antiretroviral drugs to control their HIV infection - a 54% increase in one year.
However, it is estimated that 7.1 million people in those countries could benefit from the drugs.
It also falls short of the WHO aim of getting antiretrovirals to 3 million needy people by the end of 2005.
The report found that 1.3 million HIV patients in sub-Saharan Africa are now receiving the drugs.
This represents a coverage rate in the area of 28% - compared with just 2% in 2003.
The lowest access rate - just 6% - was in the North Africa and Middle East region.
Only 11% of pregnant women with HIV are getting drugs that could prevent them passing the virus to their baby.
The report calls for prevention of mother-to-child transmission to be made a top priority.
Front-line drug prices in the world's poorer countries fell by up to 20% last year, meaning some drugs are now less than half the price they were in 2003.
The drop in prices has been put down to competition from manufacturers of generic drugs, and political pressure from the international community.
However, the report warns that second-line drugs - the next option if first-line alternatives have limited effect - are still "unaffordably high" in these countries.
Pharmaceutical companies have previously argued that antiretroviral drugs were too complex for poor countries which often lack a sophisticated medical infrastructure.
But the report shows that patients in these countries are responding just as well to the drugs as their peers in the developed world.
Dr Peter Piot, executive director of UNAids, said: "The significant progress outlined in this report in scaling up access to treatment is a positive step forward for many countries in achieving their ambitious goals of universal access to HIV prevention, treatment, care and support.
"However new data in the report also shows that there is still a long way to go, particularly in the widespread provision of treatment to prevent mother to child transmission of HIV, which remains one of the simplest and cheapest proven prevention methods available."