Police have banned political rallies and the opposition has accused the authorities of waging a violent crackdown, as Zimbabwe's political crisis deepened nearly two weeks after a presidential election that produced no official winner.

Zimbabwe's neighbors hoped to find a resolution Saturday at an emergency summit in Zambia, but it was not clear if President Robert Mugabe would even attend the meeting.

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

Tsvangirai arrived in Lusaka on Friday night with spokesman Nqobizitha Mlilo, who called for "a final solution" from southern African leaders who have notably failed to criticize Mugabe.

"Surely it must now weigh upon them that they need to find a final solution," Mlilo told The Associated Press. "Zimbabweans went to the polls, voted for change, voted for the MDC and Mr. Tsvangirai. The democratic will of the Zimbabwean people must be protected by the leaders of southern Africa."

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.

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 responding to intimidation and violence." The warning is the strongest yet from the leader of Britain, Zimbabwe's former colonial ruler.

On Friday, the police announced they were banning all such rallies.

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

Party leaders would decide Sunday whether to defy the ban and call for a general strike, said MDC spokesman Nelson Chamisa.

"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," he said.

Mazango, the police official, accused the MDC of sending activists across the country "to ignite violence" and warned them to return home, "otherwise the law will descend on them."

The opposition has accused the security forces and ruling party militants of engaging in a wave of violence against perceived opponents 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.

The black owner of a nearby farm was beaten up, the workers said, speaking on condition of anonymity for fear of repercussions.

Huts on both farms were torched, and women and children searched through the charred remains Friday, trying to salvage something of their lives.

U.S. 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 been "seemingly unable or unwilling to arrest the perpetrators," the group said.

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's policies, called an emergency regional summit.

At least 10 heads of state were expected, said Zambian Information Minister Mike Mulongoti. However, it was not clear if Mugabe would be among them.

Zimbabwe state radio said Friday evening the country would be represented by three senior ministers from its recently dissolved Cabinet. When reached by phone, outgoing Housing Minister Emmerson Mnangagwa told The Associated Press he would lead the delegation. Asked if that meant Mugabe was not attending, he declined to answer.

Deputy Information Minister Bright Matonga said earlier that no firm decision had been made, and a Zambian official, speaking on condition of anonymity, said Mugabe had initially agreed to attend but now his presence was in doubt.

Mlilo, the MDC spokesman, said Tsvangirai received a direct invitation to the meeting and that he would be a full participant, claiming the election outcome meant he was now a "head of state." Such a declaration would likely infuriate Mugabe, and could be a reason for his hesitation in attending.

Mulongoti said no decision had been made about whether Tsvangirai would address the summit or be a participant.

The United States called on the summit to "take a firm stand for democracy in Zimbabwe," McCormack said.

On a visit to the United States, South African Nobel Laureate Desmond Tutu said Mugabe should "step down with dignity."

Mugabe has traditionally enjoyed the support of other African leaders, using past meetings of the Southern African Development Community to denounce his opposition and Western leaders he accuses of plotting to topple him.

Tsvangirai said he hoped for a different outcome this time.

"We can show the world that we, Africa, can solve our own problems and safeguard democracy and the rule of law," he said in a statement.