Regional observers have said Zimbabwe's presidential poll did not reflect the will of the people, hours after Robert Mugabe was sworn in for another term.
The Southern African Development Community (Sadc) election observers said pre-poll violence had undermined the vote's credibility.
BBC regional correspondent Peter Biles says it is a major blow for Mr Mugabe.
Mr Mugabe claimed a landslide victory as the sole candidate after opposition leader Morgan Tsvangirai withdrew.
The statement from the election observers comes on the eve of a summit of African Union (AU) leaders in Egypt which Mr Mugabe is expected to attend.
OFFICIAL RESULTS
"The elections did not represent the will of the people of Zimbabwe," it said.
The head of Sadc's 400-person observer mission, Angolan Sports Minister Jose Marcos Barrica, was quoted as saying: "The pre-election phase was characterised by politically-motivated violence, intimidation and displacements."
Another observer team, from the Pan-African Parliament, has called for fresh elections to be held, saying the vote was not free or fair.
Our correspondent says the observers' reflections could lead southern African states to withhold recognition of Mr Mugabe as president and declare the election illegitimate, as some Western nations have already done.
This in turn could pressure the AU into taking some form of action, he adds.
Led by the US and Britain, there has been growing international condemnation of the presidential election run-off, which was held on Friday.
UN Secretary General Ban Ki-moon said the outcome "did not reflect the true and genuine will of the Zimbabwean people or produce a legitimate result."
But China is resisting US calls for strong action by the UN against Zimbabwe.
After meeting US Secretary of State Condoleezza Rice in Beijing the Chinese Foreign Minister, Yang Jiechi, called for dialogue between the government and opposition in Zimbabwe.
US President Bush has said he wants an arms embargo and a travel ban on government officials, but correspondents say China might veto any such calls in the UN Security Council.
Talks with opposition?
Mr Mugabe was sworn in during a quickly convened ceremony about an hour after the Zimbabwe Electoral Commission announced the results.
The commission said Mr Mugabe won 85.5% of the vote, but many ballots were spoiled.
Turnout was about 42%, it said, similar to that of the disputed first-round vote in March.
In a speech that followed the swearing-in ceremony, Mr Mugabe said he was committed to talks with the opposition to find a solution to the political crisis.
"It is my hope that sooner rather than later, we shall, as diverse political parties, hold consultation towards... dialogue as we minimise our differences and enhance the area of unity and co-operation," he said.
The mention of dialogue seems to be a response to pressure from within Africa to enter into talks with Mr Tsvangirai's Movement for Democratic Change (MDC).
Mr Tsvangirai refused to attend the inauguration, to which he was invited, and said Mr Mugabe now had no option but to negotiate.
In a BBC interview, Mr Tsvangirai said that any negotiation should be based on the result of the first-round.
Mr Tsvangirai was ahead in that vote with 47.9% against 43.2% for Mr Mugabe, falling just short of an outright majority to take the presidency.
"We believe the 29 March election reflected the will of the people," he said.
"That should be the basis upon which any negotiation... for a transition should be based."
The results from the first round took the electoral commission five weeks to release, compared with less than two days for the run-off result.
HAVE YOUR SAY
The government has blamed the MDC for the violence.
The 84-year-old Mr Mugabe has been in power since Zimbabwe gained independence from Britain in 1980.
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