The most senior United States aid official has launched a blistering attack on the policies of Zimbabwe President Robert Mugabe.

These risk turning a drought into a famine affecting half the population - six million people - said Andrew Natsios, head of the United States Agency for International Aid (USAid).

It is madness to arrest commercial farmers in the middle of a drought

Andrew Natsios, head of USAID

Despite this criticism, he announced that USAid has increased food aid to drought-stricken southern Africa by 190,000 tons.

This brings total US food assistance to the region to almost 500,000 tons - half of the total requested by the World Food Programme.

Criticism of Zimbabwe's policies also came from the US State Department's African affairs chief, Walter Kansteiner.

He said that the United States did not recognize Robert Mugabe as the democratically legitimate leader of Zimbabwe and that the US needed to work with Zimbabwe's neighbours to encourage "a more democratic outcome" in the country.

However, the row over genetically modified (GM) food aid for Zimbabwe has been solved, Mr Natsios said.

Reservoirs full

The announcement of the donation follows a warning by the head of the international children's fund, Unicef, that the world was ignoring the food crisis in southern Africa.

At least 13 million people are facing the threat of famine in the region as a result of drought, crop failures and political instability.

The seven worst-affected countries are Angola, Lesotho, Malawi, Mozambique, Swaziland, Zambia and Zimbabwe.

Zimbabwe's mechanised and irrigated white-owned farms were an "insurance policy" for Zimbabwe and the rest of southern Africa, Mr Natsios said.

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Despite the drought, reservoirs on these farms were full of water, which was not being used, he said.

But he blamed several different policies for worsening the food crisis:

• Evicting white farmers from their land
• Controlling the price of maize - meaning businesses are not importing maize into Zimbabwe for sale
• Controlling the exchange rate, which has the same effect

Mr Natsios said that people close to the president were benefiting from the redistribution of land, "so they're not exactly turning these over to poor people".

"It is madness to arrest commercial farmers in the middle of a drought, when they could grow food to save people from starvation," he said.

Genetically milled maize

Mr Kansteiner said that the US was trying with Zimbabwe's neighbours, South Africa, Botswana and Mozambique, to isolate the Mugabe government.

But Mozambican Foreign Minister Leonardo Simao denied being involved, reports Reuters news agency.

Land reform is Mugabe's major policy

"I am not aware of any initiative of that kind with us... Our approach to Zimbabwe is to bring everybody on board to find solutions," Mr Simao is quoted as saying.

Zimbabwe has responded to the US comments by accusing the Americans and Europeans of opposing the policy of redistributing farmland from whites to blacks on "racist" grounds, Reuters reports.

The US has already imposed a travel ban on Zimbabwe's leaders and frozen their foreign assets - similar to measures taken by the European Union.

Zimbabwe, Zambia and Mozambique are all concerned that some GM food aid could be planted, contaminating their own crops.

But Mr Natsios said that 17,000 tonnes of US GM maize would be exchanged for a similar amount of Zimbabwean maize.

Zimbabwe would then mill the GM maize at its own expense, to ensure that none of the maize was planted.