The number of HIV patients receiving anti-retroviral medicine has doubled in five years, the UN said.

A new report by UNAIDS said it was on course to hit a target of 30 million people on ARV treatment by 2020.

In just the last two years the number of people living with HIV on antiretroviral therapy has increased by about a third, reaching 17.0 million people -- 2 million more than the 15 million by 2015 target set by the United Nations General Assembly in 2011. Since the first global treatment target was set in 2003, annual AIDS-related deaths have decreased by 43 percent.

But the report showed the huge risks that some young women face.

Last year more than 7,500 teenagers and young women became infected with HIV every week worldwide, with the bulk of them in southern Africa.