The UK government is to invest £10.7m in researching how to prevent adolescents and prisoners, two of the most vulnerable groups in southern Africa, becoming infected with HIV.

The announcement comes as the UK reviews its Aids funding, which totalled £1bn for HIV programmes over the past three years. International development minister Lynne Featherstone, speaking to the Guardian from Malawi on Thursday, made it clear she felt there has been an imbalance in the way funds are apportioned to HIV, with prevention being relatively neglected.

"The argument I have been making is that most of the resources are going to treatment," she said.

In Malawi, 63% of people with HIV are on treatment, including lifelong medication with antiretroviral drugs for mothers, which keeps them alive and prevents transmission to their babies. "But all these things are very expensive. The emphasis has been on treatment," she said. In discussions with Malawi's president, Joyce Banda, Featherstone said: "I have asked them to look at prevention and behavioural change, and to look at women and girls and the connection to violence."

Rates of infection across southern Africa are unacceptably high, she said. "Across the world, we have made huge strides in tackling HIV over the past decade. Yet new infection rates remain too high, particularly amongst adolescent girls. It is a sad fact that this vulnerable group is being left behind.

"I want to see zero new infections, zero deaths from HIV-Aids and zero discrimination. This won't happen unless we prioritise marginalised groups. This means addressing stigma, empowering women and girls, and reducing the violence against them that makes them so vulnerable to the epidemic."

In Dedza, Malawi, Featherstone visited a health centre which has strong links to a police-run victim support unit. "When women come in to the health centre, sometimes it is clear they have been the victim of gender-based violence," she said. They can then be referred to the support unit, which will pursue the aggressor.

"They had a really excellent inspector in charge of the unit, who understood the issues around violence and women and girls," she said. "The issue is about scaling up for a whole country."

Spending on antiretroviral drugs in southern Africa massively outstrips spending on prevention, because treatment is highly successful and cost-effective since the prices of antiretrovirals dropped under pressure from campaigners and the involvement of generic drug companies. Behavioural change campaigns, on the other hand, have not had anything like the same good outcomes.

The UK's HIV strategy review will look to preventing infection as the logical way to reduce costs – while infections continue to rise, the drug bill rises too. The strategy is intended to contribute to preventing half a million new infections among women by 2015.

HIV prevalence in Malawi has dropped from 11.4% in 2008 to 10.6% this year, but young women are still bearing a bigger burden than their male counterparts. Girls are nearly twice as likely to become infected in Malawi as boys. Prisoners are also very vulnerable. Across southern Africa, it is thought that as many as 15% of people in jail have HIV.