A United Nations agency has criticised rich nations for failing to meet pledges for financial assistance as it warned that millions of people in southern Africa face food shortages.

Some 4.3 million people in southern Africa will now have to go without the aid earmarked by the World Food Programme (WFP), which blamed a £30 million gap in funds for the cuts, reports Reuters.

The cutbacks will affect mother and child nutrition centres, school feeding projects and schemes targeting HIV/AIDS and tuberculosis patients, for whom nutrition is key in boosting immunity to diseases that have ravaged the region.

Namibia, Malawi and Swaziland - which has one of the world's highest rates of infections for HIV/AIDS - will be hit severely by the reductions as they face losing between 80 and 100 per cent of their food aid.

"Due to a lack of donor support, since September WFP offices across the region have begun to reduce the level of food assistance provided to mother and child nutrition centres, school-feeding projects and patients receiving medication for HIV/AIDS or tuberculosis," said the WFP in a statement.

"Here, where HIV prevalence rates are the highest in the world, people are dying of AIDS-related illness when they could have survived for years if they had had enough food to eat. Anti-retroviral therapy is not effective on an empty stomach."

The statement also revealed that to date the WFP had only received half the US$118 million in cash contributions needed.

Around 1.4 million people were found to be in "critical need" of food aid in Zimbabwe, where the WFP said it had already been forced in October to scale back help to about half of the 900,000 people in need.

The food deficits in troubled Zimbabwe have been blamed by critics on drought and an exodus of the country's most productive commercial white farmers who fled the government's controversial land reform programme.