An angry row has erupted over Conservative calls for Tony Blair to snub Zimbabwe's president at next week's World Summit on Sustainable Development.

UK ministers insist the Johannesburg summit must not be hijacked by the controversy over Robert Mugabe's regime.

They say Tory calls to block development aid would punish all Africa for one man's "sins".

Robert Mugabe is wreaking havoc in a country that was the bread basket of southern Africa

Iain Duncan Smith Conservative leader

Conservative leader Iain Duncan Smith has urged the prime minister to boycott President Mugabe's summit speech in protest at policies causing "starvation" in Zimbabwe.

As ministers hit back at the suggestion, the Tories have pressed the government to defend lives in Africa rather than its own record.

The summit is billed as the largest conference ever, with delegates from more than 170 countries trying to build on the work of the 1992 Earth Summit, which was held in Rio de Janeiro.

Mr Mugabe is due to address the conference on 2 September an hour after Mr Blair's speech.

'Farce'

The Tories want Mr Blair to walk out of the conference room when the Zimbabwean president gets up to speak.

In a letter to the prime minister, Mr Duncan Smith warned the summit would "turn into a farce" unless it tackled the way Mr Mugabe was "systematically starving his own people, driving efficient farmers off highly productive land and forcing farm workers to live in squatter camps".

Jack Straw has accused the Tories of "cruel" ideas

The letter follows months of growing concern about President Mugabe's policy of evicting white farmers from their land.

Downing Street has reportedly dismissed the Tories' snub call, saying Mr Blair will not alter his summit plans.

Environment Secretary Margaret Beckett said it was "singularly unlikely" that Mr Blair would be shaking Mr Mugabe's hand at the meeting in Johannesburg.

'No hijacking'

But she said the summit had to focus on tackling world poverty and protecting the environment.

"We are certainly determined to make sure that the important issue of the summit and its potential to do good isn't hijacked by issues, by concerns such as those about Zimbabwe," Mrs Beckett told BBC Radio 4's Today programme.

"The Zimbabwean Government is under no illusion about the British attitude to the policies that they have been pursuing.

Mugabe's policies are being blamed for food shortages

"Indeed, some of the rudest things that have ever been said about Tony Blair have been said by Robert Mugabe because of the British Government's opposition."

In his letter, Mr Duncan Smith pressed ministers to make clear that UK funding for Nepad, the African aid plan, should be reflected by "effective action" by African nations against President Mugabe.

That suggestion prompted an angry response from Foreign Secretary Jack Straw, who said the Mugabe regime never benefited from Nepad anyway.

"Not only would it hinder attempts to isolate Mugabe, but its cruel effect would be to punish the whole of Africa for the sins of one man," said Mr Straw.

Later, shadow foreign secretary Michael Ancram said his counterpart "should stop making excuses for his own inaction".

The Tory MP said the summit should not just be about Zimbabwe but the problem had to be addressed in the final communiqu�.