Mr Mugabe has come under international pressure over the poll
Zimbabwe's ruling party has rejected criticism of its leadership by former South African President Nelson Mandela.
Mr Mandela said Zimbabwe was suffering a failure of leadership ahead of a run-off presidential poll from which the opposition has withdrawn.
A ruling Zanu-PF official described Mr Mandela's comments as unacceptable and unfortunate for a man of his stature.
Southern African leaders have called on President Robert Mugabe to postpone the vote and negotiate with the opposition.
The leaders from the Southern African Development Community (Sadc) said conditions did not permit a free and fair election on Friday.
Speaking to the BBC, the parliamentary chief whip for Zanu-PF said Mr Mandela's statement was "very unfortunate".
"I don't see the merit in that kind of statement... [It's] totally unacceptable... the judgement that he has made," Jerome MacDonald Gumbo said.
Asked whether the final round of the presidential vote would be postponed, he said: "There is no chance of that. There is no reason."
Opposition Movement for Democratic Change (MDC) leader Morgan Tsvangirai pulled out of the election on Sunday, over fears of increasing political violence.
Mr Mugabe came second to Mr Tsvangirai in the first round of the presidential vote in March.
Since then, the MDC says some 86 of its supporters have been killed and 200,000 forced from their homes by militias loyal to Zanu-PF. The government blames the MDC for the violence.
President Mugabe, who will address his final campaign rally on Thursday, said his government was open to negotiations with "anyone", but only after the vote.
Mr Tsvangirai said negotiations would not be possible if Mr Mugabe went ahead with the run-off.
Speaking to the UK's Times newspaper by telephone, Mr Tsvangirai said of Mr Mugabe: "How can you call yourself an elected president? You are illegitimate and I will not speak to an illegitimate president."
Despite Mr Tsvangirai's withdrawal, Zimbabwe's election authority says Friday's vote will go ahead because his letter of notice came too late.
A BBC contributor in the southern town of Masvingo said army chief of staff Major General Engelbert Rugeje told a rally that his soldiers would force members of the public to go vote for Mr Mugabe.
"We are soldiers who do not ask for things, but force things," Maj Gen Rugeje said. "On Friday, we are going to make sure that you go and vote not for a person of your choice, but Mugabe."
Zimbabwean journalist Brian Hungwe also told the BBC that hundreds of people had sought shelter in the South African embassy in Harare, asking for political refuge.
The crisis has drawn growing international condemnation of Mr Mugabe and his government.
The US has said it will not recognise the results of the vote.
Speaking at a dinner in London on Wednesday to mark his 90th birthday, Mr Mandela said: "We watch with sadness the continuing tragedy in Darfur. Nearer to home we have seen... the tragic failure of leadership in our neighbouring Zimbabwe."
They were the former leader's first comments on the crisis.
Mr Mandela had held his silence until now, says the BBC's diplomatic correspondent James Robbins, to avoid undermining the efforts of South Africa's President Thabo Mbeki as chief mediator on Zimbabwe.
Mr Mbeki's policy of "quiet diplomacy" has been criticised for its failure to resolve the crisis in Zimbabwe.
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