Mr Tsvangirai was arrested several times ahead of the run-off
Zimbabwe's opposition leader Morgan Tsvangirai has rejected forming a unity government if he is not recognised as the winner of presidential elections.
African leaders called for a unity government days after Robert Mugabe won a run-off boycotted by the opposition.
Mr Tsvangirai, who won the first-round vote, said the African Union should appoint another mediator to join South Africa's leader Thabo Mbeki.
Earlier, a spokesman for Mr Mugabe welcomed the AU call for dialogue.
The opposition Movement for Democratic Change (MDC) leader withdrew from last week's poll citing widespread state-sponsored violence.
In a statement, the MDC said Tuesday's resolution by African Union leaders did not adequately deal with the ongoing violence in Zimbabwe, which include reports of reprisal attacks on those who failed to vote for Mr Mugabe on Friday.
At the end of a two-day summit, which ended in Egypt on Tuesday, AU leaders approved a resolution calling for the "creation of a government of national unity" in Zimbabwe.
Mr Tsvangirai said the resolution did not acknowledge the illegitimacy of the 27 June run-off vote.
"The resolution endorses the concept of a government of national unity, without acknowledging that the MDC, as the winner of the last credible election on 29 March, should be recognised as the legitimate government of Zimbabwe."
He said the basis of talks should be the first-round election.
"A government of national unity does not address the problems facing Zimbabwe or acknowledge the will of the Zimbabwean people," he said.
"While the MDC remains committed to negotiations, this must be based on the 29 March result and must move towards a transitional agreement," AFP news agency quotes him as saying.
Information Minister Sikhanyiso Ndlovu said Mr Mugabe had already called for dialogue before the Sharm el-Sheikh meeting.
"It is only endorsing what the president said, that he is going for national dialogue and is open to anyone who is willing to talk, not national unity concocted by the West," he said.
After the AU meeting, French Foreign Minister Bernard Kouchner, whose country holds the European Union's rotating presidency, said the EU "will not accept a government other than one led by Mr Tsvangirai".
But Mr Mbeki said solutions could not be imposed from outside.
"The result that comes out of that process of dialogue must be a result that is agreed by the Zimbabweans," he told the South African Broadcasting Corporation.
Militias on rampage
Since last Friday's run-off, the MDC says nine of its supporters have been murdered, hundreds more beaten and forced to leave their homes.
In Manicaland alone 500 MDC supporters and families have been forced to flee their homes since the weekend and are now seeking refuge at the party's headquarters in Mutare, it said.
Zimbabwean journalist Themba Nkosi told the BBC that ruling party militias known as the "Green Bombers" have been on the rampage in the southern city of Bulawayo targeting commuter taxi operators and drivers.
The militias are accusing the drivers of failing to campaign for Zanu-PF after being allocated free fuel by the party at government-owned filing stations, he says.
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