Gangs of Zanu-PF supporters roamed the countryside burning houses, abducting workers and beating and burning anyone suspected of supporting the opposition party, the Movement for Democratic Change.

Hopes that the return of white farmers to their properties and the intervention of police in land occupations at the weekend signalled a gradual return to normality were dashed as violence flared in rural areas, sparking an exodus of hundreds of farm workers.

Most bore physical evidence of having been brutally beaten by squatters. Several were in hospital in the provincial centre of Marondera, near where the first murder of a white farmer took place 10 days ago.

One farmer was seen taking about 10 workers, with bruises on their hands, legs and backs, to hospital in his pickup truck. "The trouble is that we are not in a position to help our workers," he said.

Ishmael Mutengiwa, a labourer from a farm 75 miles east of the capital, and his wife, Farirai, were both badly burned after a gang of self-styled war veterans burned down their home. Mr Mutengiwa suffered suffered severe burns to his hands while he struggled to open the front door, which was locked from the outside, and his wife's face was burned.

"We were sleeping... [they] put grass in the house and poured petrol and lit the fire," Mr Mutengiwa said. "They said we must die because we are MDC. They said this is Mugabe's country."

Another farm worker said he had been picked up by a gang of squatters on Sunday night and forced to join them: "They beat us and told us to follow them to the next farm. We were forced to beat our own friends."

A black foreman who was taken away in handcuffs on Sunday was still missing yesterday.

Though in some areas police followed the squatters without intervening, 60 miles north of the capital a farm manager, his girlfriend and another woman were freed after officers ordered 700 veterans to end a one-day siege of their farm.

Officers also escorted 45 farmers and their families back to to the Macheke district near Marondera yesterday morning. "They are taking an active role. "There has been a definite change in the last 48 hours," said Tim Henwood of the Commercial Farmers' Union.

Mike Moon, a farmer, said: "Pressure has eased off us and been transferred onto labour. There is constant beating of labourers every night. We are powerless to do anything."

The switch in tactics pointed to the growing desperation of President Mugabe and his party in the run-up to elections, which were due to be held some time next month but are now likely to be delayed. The targeting of black farm workers, who are among the most poorly paid in the country, means there is no longer any pretence that the wave of violence across Zimbabwe has been prompted by a desire for land or racial hatred.

Mr Mugabe has endorsed the land occupations, which have left five MDC activists, two white farmers and a policeman dead. Last week he branded white farmers "enemies of the state" for backing the MDC.