The situation became murkier late on Monday when Zimbabwean police announced they had arrested seven election officials for undercounting votes cast for Mugabe in four provinces.
"We're still investigating, but we have established that there was deflation of figures in respect of one candidate ... the ZANU-PF presidential candidate (Mugabe)," police spokesman Wayne Bvudzijena said.
RUN-OFF LOOMS
The opposition and Western powers blame Mugabe for reducing the once prosperous country to misery by economic mismanagement.
Zimbabwe has inflation of more than 100,000 percent - the highest in the world - an unemployment rate above 80 percent and chronic shortages of food and fuel. The Zimbabwean dollar is a virtually worthless currency.
Millions of its people have fled into exile.
Tsvangirai wrote in Britain's Guardian newspaper on Monday: "Major powers here, such as South Africa, the U.S. and Britain, must act to remove the white-knuckle grip of Mugabe's suicidal reign and oblige him and his minions to retire."
Mbeki, who failed last year to mediate an end to the crisis, said last weekend the post-election situation was "manageable".
Although Tsvangirai is demanding Mugabe step aside, ZANU-PF and independent monitors' projections show the challenger failed to win an absolute majority despite outpolling Mugabe and will be forced into a run-off.
Electoral rules say a runoff must be held three weeks after the release of results, meaning the longer the delay the more time Mugabe and his supporters, which include a group of liberation war veterans, have to regroup.
The re-emergence of the former soldiers, often used as political shock troops by Mugabe, has increased concern he plans a violent response to his election setback.
The veterans led a wave of violent occupations of white farms as part of a government land redistribution programme that began in 2000, and some Mugabe opponents say they have again begun occupying farms to intimidate those loyal to the MDC.
"It's basically happening the same way it happened in 2000 and thereafter, where groups of people come to your farm and tell you to leave your business and equipment," said Trevor Gifford, president of the Commercial Farmers' Union.
Meanwhile in Harare two Western journalists arrested last Thursday were granted bail on Monday, though a lawyer for New York Times correspondent Barry Bearak said he had been taken to hospital after suffering back injuries in a fall in jail.
Bearak, a Pulitzer Prize winner, and a British reporter were arrested at their hotel and charged with covering the election without accreditation.
