The shadow foreign secretary has condemned the Zimbabwean government for its role in spreading instability to surrounding countries.

Michael Ancram's comments came as white farmers in Zimbabwe were told by president Robert Mugabe that they would be removed from their land.

"We set ourselves an August deadline for the redistribution of land and that deadline stands," Mugabe said in a keynote speech marking a national day of honour for those who fought in the country's battle for independence.

The current stand-off between the government and the farmers has seen court orders to surrender land ignored.

So far only about 500 of the 2900 white farmers have vacated their land, despite the passing last Thursday of the government-imposed deadline. Many appeared to have been hoping that the growing food shortages across southern Africa would give them extra leverage in their attempts to hold on to their land.

But the Zimbabwean government has dashed their hopes, vowing to press ahead with reforms which it says are necessary to address the legacy of colonialism under which much of the best farming land is white-owned.

The Conservatives, however, condemned the often violent tactics used to seize control of the land. Michael Ancram said it was time to step up the pressure on Robert Mugabe.

"The world has got to say to them that this type of behaviour - the murder, the mayhem, the obscenity of starvation on the one side against agricultural land which could be producing food laying idle on the other - this is simply not on," he told BBC Radio 4's Today programme.

And he warned that the crisis in Zimbabwe was spilling over into the surrounding countries, with South Africa, Botswana and Malawi all suffering from the political instability and food shortages.

"They know that Mugabe is causing problems for them as well," Ancram said.

"What we have got to do, the whole international community, has got to say if we are going to work to help Africa then Africa has to help itself as well. They can't have this situation in Zimbabwe continuing."

The shadow foreign secretary also urged the British government to lead protests against president Mugabe's policies at the forthcoming sustainable development conference in neighbouring South Africa.

"We have got to stop shillyshallying," Ancram told the BBC. "We have got the Earth summit coming up in Johannesburg. Tony Blair is going to be nearer to Zimbabwe than he has been for a very long time.

"Mugabe and his people, I think, will be out in Johannesburg. They have got to be faced out."