Reports suggest a large number of spoiled ballot papers
Robert Mugabe is expected to be sworn in as Zimbabwe's president on Sunday, following his victory in an election boycotted by the opposition candidate.
Government sources say Mr Mugabe has won by a huge margin in the vote, which has been widely condemned as a sham.
Morgan Tsvangirai withdrew from the election amid claims of violence and intimidation by government supporters.
US President George W Bush said he had ordered sanctions be drawn up against the "illegitimate" government.
In a statement, Mr Bush said his secretaries of state and the treasury were working on the penalties. He added he would press for international action, including an arms embargo.
He said the move was in response to "the Mugabe regime's blatant disregard for the Zimbabwean people's democratic will and human rights".
Election officials in Zimbabwe say that the vote count is now complete, and they hope to announce the result later on Saturday.
The Pan-African parliament observer mission in Zimbabwe said there had been many spoilt ballots, and in some areas these appeared to outnumber votes cast for President Mugabe.
Zimbabwean journalist Brian Hungwe says that in some cases, voters expressed their anger against the violence by calling Mr Mugabe a murderer on the ballot papers.
Contrary to the state-run newspaper's report of a massive turnout in Friday's election, the head of the observer mission said turnout had been "very, very low".
Mr Tsvangirai, leader of the Movement for Democratic Change (MDC), announced he was pulling out of the election on Sunday.
But his name remained on ballot papers after Zimbabwe's electoral authorities refused to accept his decision.
Meanwhile, diplomatic efforts are continuing to try to find a solution to the crisis.
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If the UN doesn't intervene this time we are truly damned
Kenyan Foreign Minister Moses Wetangula has said sanctions against Zimbabwe are unlikely to work, and that Mr Mugabe and the opposition should instead be encouraged to talk.
He was speaking at a meeting of African Union (AU) foreign ministers in the Egyptian town of Sharm el-Sheikh, before a full meeting of heads of state on Monday which Mr Mugabe is expected to attend.
The BBC's Elizabeth Blunt, in Sharm el-Sheikh, says the AU's traditional preference for conciliation and consensus makes the idea of some kind of government of national unity popular among delegates.
She says there are hopes that Mr Mugabe may be more amenable to this now he can come to the table as the victor in the presidential run-off, rather than an also-ran from the first round of voting.
The UN Security Council is expected to return to the issue of Zimbabwe in the coming days. However, diplomats say that because of resistance from South Africa, China and Russia, the council is unlikely to impose sanctions.
On Friday, the UN Security Council said it deeply regretted Zimbabwe's decision to go ahead with the presidential poll.
It said conditions for a free and fair election did not exist, but - after objections from South Africa - stopped short of saying it was illegitimate.
The Zimbabwe Election Support Network, a monitoring group, reported that people in most rural areas had been forced to vote in Friday's poll.
A Zimbabwean journalist said militias loyal to Mr Mugabe had gone door-to-door in townships outside the capital, Harare, to coerce people.
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.
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