HARARE, Zimbabwe — Police banned political rallies on Friday as the crisis deepened over Zimbabwe's unresolved presidential election, with a senior police official warning that anyone who defies the order "will be dealt with severely."

The opposition said it was considering whether to defy the ban and call a general strike.

"We cannot accept a declaration of a police state," said Nelson Chamisa, spokesman for the opposition Movement for Democratic Change. "People have just voted for change, for democracy and what do they get? This is unacceptable. This is ridiculous."

The developments came as British Prime Minister Gordon Brown said the international community's patience with Zimbabwe's regime was "wearing thin."

Brown said he was "appalled by the signs that the regime is once again resorting to intimidation and violence." The comments were the strongest yet from the leader of Britain, Zimbabwe's former colonial ruler.

Zimbabwe's opposition accused President Robert Mugabe's regime of waging a violent crackdown in an attempt to keep power, two weeks after a presidential election that produced no official winner.

Zimbabwe's neighbors hoped for a resolution Saturday at an emergency summit in Zambia, but it was unclear if Mugabe would even attend.

Official results from the March 29 election have yet to be released. Independent tallies suggest Mugabe lost, but that a runoff would be needed because no one won more than 50 percent of the vote.

Opposition leader Morgan Tsvangirai says he won outright and has traveled the region in recent days asking neighboring leaders to push for Mugabe to resign after 28 years in power.

In an interview from Botswana, Tsvangirai implied he feared returning home, saying he was a "prime target" for security forces. He told the South African Broadcasting Corp. that he hoped the summit would "create new circumstances to calm the situation down and create a safe environment for me to go back."

Tsvangirai's Movement for Democratic Change has held no major protests since the vote, but party officials had planned a rally Sunday, a day before an expected High Court ruling on their petition to force the release of the results.

But police said they were banning all such rallies.

"All political parties are warned against creating mayhem," said Senior Assistant Police Commissioner Faustino Mazango. "Surely those who want to provoke a breach of peace, whoever they are and whatever office they hold, will be dealt with severely."

The opposition has accused security forces and ruling party militants of inflicting violence on perceived opponents since the election to intimidate voters and ensure Mugabe wins a runoff.

In the northern town of Centenary, about 140 miles north of Harare, militants attacked workers on at least two black-owned farms Thursday night, assaulting them and burning their huts, the workers said.

Ruling party officials had encouraged militants to invade the country's few remaining white-owned farms, saying they were trying to protect Zimbabweans from encroaching colonialism. Opposition officials say such attacks are a smoke screen for assaults on mainly black opposition supporters.

Workers on the Mount Panis farm lost all their belongings when a gang of about 50 men attacked them during the night, accusing them of being MDC supporters, the workers said. Several were hospitalized and many fled into the nearby mountains or to neighboring farms.

State Department spokesman Sean McCormack said Washington had "credible reports of violence and intimidation" against opposition supporters and called on the government to end the attacks.

Amnesty International said the violence suggested a program of "coordinated retribution against known and suspected opposition supporters," and Human Rights Watch said it had received "credible information of dozens" of such attacks over the past week.

Police have arrested many opposition supporters as well, including Tsvangirai's lawyer, Innocent Chagonda, who was detained Thursday, MDC officials said.

In an effort to end the crisis, Zambian President Levy Mwanawasa, the only southern African leader to publicly criticize Mugabe, called an emergency regional summit.

At least 10 heads of state were expected, said Zambian Information Minister Mike Mulongoti.

Zimbabwe state radio said the country would be represented by three senior ministers from its recently dissolved Cabinet, making no mention of Mugabe's possible attendance. Outgoing Housing Minister Emmerson Mnangagwa told The Associated Press he would lead the delegation. When asked if that meant Mugabe was not attending, he declined to answer.

MDC spokesman Nqobizitha Mlilo said Tsvangirai would participate, claiming the election outcome meant he was now "head of state."