"We need to embark on mass action to bring the government to its senses," said Morgan Tsvangirai, leader of the Movement for Democratic Change. He spoke about the plans to ask labor groups to prepare for the campaign following an emergency meeting of party officials.
Earlier Saturday, war veterans and militants of the ruling party armed with clubs and iron bars broke up a peace rally called by the National Constitutional Assembly, an alliance of civic groups.
The rally was aimed to protest worsening political violence over land that has left at least 18 opposition supporters deadincluding three white farmers. War veterans and violent squatters have been illegally occupying more than 1,000 white-owned farms for months, saying the land disparity between whites and blacks is unacceptable.
Scores of police, some in riot gear, watched passively as militants chased at least 100 people away from a sports arena in western Harare. Others approaching were turned away by armed militants.
National Constitutional Assembly spokesman Tendai Biti said the alliance had received police permission to hold the rally.
"It is our constitutional right to meet," Biti said. The ruling Zimbabwe African National Union Patriotic Front "forced our people to disperse. They are the sponsors of violence."
Also Saturday, the state-controlled Herald newspaper quoted the country's Citizenship Office as saying that whites who never formally renounced their British citizenship were not considered true Zimbabweans and should surrender their Zimbabwe passports.
Zimbabwe banned dual citizenship in 1984. Britain, however, allowed Zimbabweans of British descent to keep their British passports. That right could only be officially renounced at a sworn ceremony before British officials, a step few whites took.
Zimbabwe's President Robert Mugabe on Friday ordered for the first time an end to the farm invasion violence, and announced the creation of a committee to distribute white-owned farmland to blacks.
The farm occupations began in February, when the government lost a constitutional referendum that would have entrenched Mugabe's powers and allowed the government to seize white farms without paying compensation.
Mugabe has said the land seizures are acceptable in a country where one-third of the fertile land is owned by a few thousand whites.
He told a news conference Friday that independence war veterans who have occupied hundreds of white-owned farms since February would not leave until a start had been made on redistributing land earmarked for landless blacks.
He said a land committee including representatives of government, the war veterans' association and the mainly white Commercil Farmers Union (CFU) would be set up to manage the redistribution of what he called "identified land."
Under the plan, the government will be bale to seize identified lands, and will reimburse the white owners only when Britain resumes payments to a land reform fund. Britain has offered to begin those payments again once the violence ceases.
By ANGUS SHAW