Jack Straw has warned that Robert Mugabe is "leading his country to ruin".

The foreign secretary said that Mugabe is the source of his country's problems and warned that the UK would not stand by and watch him reduce his people to starvation.

"The decline in Zimbabwe's fortunes has been swift and devastating," he said in an article in The Observer. "In the name of his 'land reform' policies Mugabe is reducing his people to starvation.

"A fraudulent election earlier this year was characterised by murder and intimidation. His continuing use of state-organised violence since then underlines his determination to hold on to power at all costs."

He said Zimbabwe had become "a self-made pariah, not a colonial victim".

Straw said that the UK was acting to halt the crisis but rejected opposition calls for a more direct response.

"The opposition is proposing that we force countries in the region to take further action against Mugabe by threatening to suspend our support for a vital new programme. The New Partnership for Africa's Development (NePAD) marks a different approach to Africa's problems," he said.

"African leaders developed the plan, recognising that they - not the outside world - must resolve the continent's problems. In return for increased development assistance, more debt relief and greater opportunities for trade, African governments are embarking on political and economic reform."

He said it was "scarcely credible" that the Tories suggest the government qualifies its support for this plan.

"In doing so, we would in effect hold an entire continent responsible for the sins of one man. Our aim must be to isolate Mugabe, not his neighbours," said Straw.

But he warned that the government would continue to engage with the region. "Mugabe can only defy world opinion at tremendous cost to his own people. Africa and Zimbabwe deserve better," he said.

"We will continue the path of tough sanctions and generous aid, and work resolutely with the region, Europe and the US to ensure Zimbabwe gets the legitimate and democratic government it so desperately needs."