Zimbabwe's police warned political parties against "creating mayhem"
Zimbabwean police have banned political rallies "with immediate effect", amid growing tension over the country's disputed presidential election.
The decision came amid confusion over whether President Robert Mugabe would attend a regional summit on the crisis, in Zambia at the weekend.
The results of the election, held 13 days ago, have yet to be released.
The opposition Movement for Democratic Change has called for a strike starting on Tuesday to pressure the authorities.
The MDC's leader, Morgan Tsvangirai has said he will not take part in any second, run-off presidential poll with Mr Mugabe.
"Mugabe has deployed the military in the provinces, in the districts. People are being beaten up," he told BBC Radio 4's World At One programme.
"In other words, he is creating a new electoral environment that is neither free nor fair.
"Secondly, he has been interfering in the work of the Zimbabwe Electoral Commission by arresting Zimbabwe Electoral Commission officials, by interfering with its work, and also by manipulating the result."
Workers on two farms said they were attacked by pro-government militants
Workers on at least two black-owned farms in the northern town of Centenary have said they were attacked and their huts set alight by militants accusing them of being MDC supporters.
US state department spokesman Sean McCormack said that the US embassy in Harare had received "credible reports of violence and intimidation" against opposition supporters and urged the government to let people to "exercise peacefully their political rights".
The MDC has said Mr Tsvangirai won more than 50% of the vote, and has launched proceedings in the High Court to force the election result's publication. A judgement is expected on Monday.
The ban on political rallies across the country comes two days before a planned demonstration by the MDC in the capital Harare.
No official reason has yet been given by the government for the ban, but state radio suggested that the police did not have sufficient manpower.
State radio quoted police spokesman Wayne Bvudzijena as saying most of its officers were still guarding ballot boxes from the presidential election.
But the BBC's Peter Biles in Johannesburg says the MDC will see the ban on rallies as further evidence to back up its claims that there has been an increasing militarisation of Zimbabwean society since the elections.
"All political parties are warned against creating mayhem, as we know there are many people who wish Zimbabwe to lose its peace," Senior Assistant Police Commissioner Faustino Mazango told the Associated Press news agency.
"Those who want to provoke a breach of peace, whoever they are and whatever office they hold, will be dealt with severely."
Mr Mazango accused the MDC of "spoiling for a fight", saying it had sent 350 activists to several bases to "ignite violence" and warned them to return home.
MDC spokesman Nelson Chamisa responded: "We cannot accept a declaration of a police state. People have just voted for change, for democracy and what do they get? This is unacceptable."
Saturday will see members of the 14-nation Southern African Development Community (SADC) convene in the Zambian capital, Lusaka, for talks about Zimbabwe's post-election deadlock.
But in an apparent snub to the SADC and Zambian President Levy Mwanawasa, Zimbabwean state radio said President Mugabe would be represented by three ministers.
Deputy Information Minister Bright Matonga had earlier said the summit had been "called without consultation with the Zimbabwean government".
But Information Minister Sikhanyiso Ndlovu told the BBC's Focus on Africa programme that Mr Mugabe would, after all, attend the SADC meeting.
"It's normal that when such a meeting is convened all heads of state attend," he said.
He added that it was important to remember that the grouping had a policy of non-interference.
Ahead of the summit, UN Secretary-General Ban Ki-moon congratulated the SADC for "their timely initiative" and for "mobilising and co-ordinating to help Zimbabwe overcome its post-electoral crisis through peaceful means".
"The secretary-general is concerned that the situation in Zimbabwe could deteriorate if there is no prompt action to resolve this impasse," UN spokeswoman Marie Okabe said.
The US state department meanwhile called upon SADC leaders to "take a firm stand for democracy".
"We believe that the SADC does have leverage with Zimbabwe and that they can use that leverage to positive effect on behalf of the people," Mr McCormack said.