Zimbabwe's main opposition leader has accused President Robert Mugabe of preparing to use violence against his own people ahead of a possible run-off election.

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Morgan Tsvangirai, leader of the main opposition Movement for Democratic Change party, addresses a press conference in Harare on Saturday. ((Tsvangirayi Mukwazhi/Associated Press))

Morgan Tsvangirai spoke shortly after police blocked the entrance to Zimbabwe's High Court building in Harare, preventing lawyers for his Movement for Democratic Change party from entering and pressing for the publication of presidential election results.

"Violence will be the new weapon to reverse the people's will," said Tsvangirai, who accused Mugabe of mobilizing armed militias. A group of pro-Mugabe war veterans marched through Harare on Friday.

"We know that thousands of army recruits are being recruited, militants are being rehabilitated and some claiming to be war veterans are already on the war path."

The MDC party wants the court to force Zimbabwe's electoral commission to publish the tally of the March 29 presidential vote. 

Results from legislative elections the same day, already released, show the MDC won, and early reports suggest the MDC also took the presidential vote, though not necessarily with the 50 per cent plus one majority required to prevent a runoff.

MDC lawyer Andrew Makoni said the case has been postponed until Sunday. He said the commission had asked for more time to file papers contesting the request.

Observers needed: British PM

The opposition party has also appealed for the United Nations to intervene to prevent bloodshed.

South African President Thabo Mbeki urged patience as he arrived for a meeting of government leaders in London on Saturday.

"We'll see what results come out. Both Tsvangirai and Mugabe, they have said in the event nobody has the majority, they are quite ready for a second round," said Mbeki.

British Prime Minister Gordon Brown, who is hosting the meeting, said he believed international observers should be in place if a run-off election is held.

ZANU-PF said on Friday that it is endorsing Mugabe for a run-off presidential vote, which some media reports say could be held within three weeks.

More delays expected

However, the Zimbabwe Independent newspaper on Friday said that Mugabe wanted to use his presidential powers to amend the Electoral Act to extend the run-off period to 90 days and rule by decree in the interim.

Diplomats in Harare and at the UN said Mugabe was planning to declare a longer delay before holding a runoff vote to give security forces more time to clamp down on the opposition.

A series of police raids on opposition offices were carried out on Thursday, a day after the returns from the legislative election showed Mugabe's party had lost control of the parliament's 210-member lower house.

MDC spokesman Nelson Chamisa said he's hoping the international community will do something to prevent the intimidation of the opposition and its supporters.

"They are trying to set up the context for unleashing violence. The vampire instincts of this regime are definitely going to come out," he said.

Mugabe has ruled Zimbabwe since his guerrilla army helped bring about the country's independence from Britain in 1980.

Zimbabwe suffered a severe economic slide following the often violent seizures of white-owned commercial farms during a land reform program that began in 2000.

A third of the population has fled the country, while 80 per cent of those who remain are jobless.

With inflation raging at more than 100,000 per cent, authorities introduced a new 50-million bank note on Friday, worth about $1 US and enough to buy three loaves of bread.

With files from the Associated Press