South Africa is not involved in a United States plan to oust Zimbabwean President Robert Mugabe, a senior government official has said.

But South Africa has intervened on behalf of two of its citizens arrested in Zimbabwe for defying government eviction orders, Deputy Foreign Minister Aziz Pahad told Reuters news agency.

There can never be a policy for South Africa to replace any government

Aziz Pahad Deputy Foreign Minister

Earlier this week, the most senior US expert on Africa said that the US was working with South Africa, Mozambique and Botswana to isolate Mr Mugabe in the region.

Analysts say that South Africa could hold the key to Zimbabwe's future and President Thabo Mbeki has been widely criticised for being too soft on Mr Mugabe.

Mr Mugabe and other Zimbabwean leaders are already the subject of a travel ban and have their foreign assets frozen by both the US and European Union following his controversial re-election earlier this year.

Blistering attack

"There can never be a policy for South Africa to replace any government... to discuss with anybody about how to replace another government," Mr Pahad told Reuters.

Mozambique has also denied any involvement.

"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," Reuters quotes Foreign Minister Leonardo Simao as saying.

Production has stopped on many white-owned farms

The US State Department's African affairs chief, Walter Kansteiner, said on Tuesday that the US did not recognise Mr Mugabe as Zimbabwe's legitimate leader.

"We're continuing to work with the South Africans and the Botswanans and the Mozambicans on what are some of the strategies that we can use to isolate Mugabe in the sense that he has to realise that the political status quo is not acceptable," he said.

The chief whip of Mr Mugabe's Zanu-PF party has also dismissed the US attacks on Zimbabwe's Government.

"The Americans don't even know where Zimbabwe is," Jerome Gumbo told the BBC's Focus on Africa programme.

"It is very unfair, especially coming from the administration of George Bush, which came to power in a very strange way," he said.

'Madness'

The most senior United States aid official also launched a blistering attack on the policies of President 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).

The mechanised, irrigated white-owned farms were an "insurance policy" for the entire region, he said.

Despite the drought, reservoirs on these farms were full of water, which was not being used, Mr Natsios 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

"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.

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.

Invalid evictions

Among the 215 white farmers arrested so far for not leaving their land two are South Africans.

Six South African-owned farms have been listed for acquisition and Mr Pahad said that Pretoria's High Commissioner in Harare is in touch with the Zimbabwe Government about them, but he would not say whether Mr Mugabe was being asked to exempt their farms from the land redistribution programme.

At least 215 white farmers have been arrested

South Africa is by far the biggest economy in southern Africa and has been badly hit by the Zimbabwe crisis, with some investors fleeing the entire region.

In another development, Zimbabwe's state lawyers have admitted that eviction orders served on 30 farmers had lapsed and so were invalid.

Lawyer Lewis Uriri told BBC News Online that this meant the government had to start again with the process of evicting those farmers.

He was not aware of any of the 30 being arrested.

Farmer Colin Shand says this he was arrested and ordered to leave his farm even though his eviction order had been declared invalid.

Click here to read Colin Shand's diary