White farmers in Zimbabwe's agricultural heartland resolved to strike yesterday after another member of their community was killed. The 180 farmers in the Karoi area, north-west of Harare, said they were stopping work because police had failed to curb the latest outbreak of squatter violence. They were furious after a police chief responded to their complaints with threats of "war".

Forty-six farms in the Shamva area have already been closed in protest at action by black militants, who have stepped up their intimidation campaign amid impatience over government promises of land reform. Landowners in Mazowe, Concession, Marondera and Tengwe have also threatened to follow suit. Three hundred or more farms could soon be on strike in action which could badly hit the national economy.

Since squatters began their invasions in February, five white farmers have been killed in the violence, and on Sunday night another man, Willem Botha, who was in his sixties, was beaten to death by suspected robbers. Although squatters were not accused of involvement, other farmers blamed his death on the "breakdown of law and order" caused by the land invasions, which have been encouraged by President Robert Mugabe.

In Karoi, farmers and their black employees have been subjected to constant harassment this year. More than 1,000 cases of assault have been reported to the police, but not one arrest has been made. Trouble over the past few days has pushed the local farmers' association into action.

On the Vuka estate, Fin and Jane O'Donoghue awoke with their three children yesterday to find that squatters had barricaded them inside their home. "They said no one would be allowed in or out," said Mrs O'Donoghue. "They started forming up in ranks. It looked like some military manoeuvre was beginning." The couple managed to flee with their 11-year-old daughter and sons, aged five and 10. Alarmed by their inability to make radio contact with the O'Donoghues, 15 neighbours demanded action from a local police chief, Supt Mabunda, and told him of their plans for a strike. According to farmers who met him, Supt Mabunda told them: "Do you want war? If you want war, I will bring troops and we can have war. I think we will have war today."

They accused Supt Mabunda of collaborating with the squatters, although he managed to defuse the situation at Vuka two hours later. One farmer said: "Mabunda has been behind this all along. He went and told those guys to lay off for the day and come back tomorrow."

On nearby Kutepa farm, Craig Stirling made three attempts to drive his tractor to his fields but was stopped by squatters each time. On Nassau farm, invaders ordered Dave Penny to stop all work. When he tried to take his tractors to the fields, they threatened to burn the vehicles.

Karoi is Zimbabwe's most fertile corner. Its lush fields of wheat, maize, tobacco and soya beans will be silent today. Irrigation systems will be switched off and crops will neither be reaped nor sown. Mr Penny said: "It's going to have a great effect on the economy. We have to do it and we have nothing to lose now."