Former US president Bill Clinton and Microsoft boss Bill Gates said inadequate access to treatment and continued discrimination were among the biggest problems in combating the AIDS epidemic, in addresses to the largest ever AIDS conference under way in Toronto.
"We've got to continue to fight the stigma and stop people from being scared to know their status," Clinton told the conference.
Both Clinton and Gates have donated billions of dollars to combat the spread of AIDS through foundations they founded.
Unicef spokeswoman Helga Kuhn told the conference that AIDS orphans were the "problem of the future", as the organisation predicts there will be almost 16 million AIDS orphans by 2010, up from 12 million at the end of 2005.
A new Unicef report highlights the horrendous cycle of infection and poverty that has plagued African countries. Many young children are living with chronically ill parents, forcing them to give up schooling to begin working at very early ages and care for their parents.
Such households continue to spiral further into poverty and are often the subject of discrimination from others in their village, the report says.
Doctors, nurses and teachers are also suffering or dying from the AIDS virus, further affecting health and education services in third-world countries.
Gates called the AIDS epidemic the most "brutal" illness affecting the world. Both Clinton and Gates emphasised the importance of improving access to already existing treatments in third-world countries.