South African President Thabo Mbeki has arrived in Harare for talks with his Zimbabwean counterpart, Robert Mugabe, and the opposition's Morgan Tsvangirai.
Mr Mbeki has been mediating between the two sides which have been holding talks in South Africa for more than a week.
Despite a news blackout imposed on the discussions, reports suggest a power-sharing deal may be close.
Zimbabwean government spokesman George Charamba said a "milestone" had been reached but did not elaborate.
He told state media that Mr Mbeki was "going to meet the principals, basically to update them on the progress so far and to consult on how to take the dialogue forward.
"This is an important milestone that has been registered in the interparty dialogue," he added.
Mr Mugabe won a run-off in June after Mr Tsvangirai pulled out of the race alleging violence against his backers.
South African mediators say that talks are aimed at creating some form of coalition but there is disagreement over who would lead a unity government and over Mr Mugabe's exact role.
Mr Mbeki is expected to return to South Africa on Sunday afternoon.
South Africa's media report that the power-sharing deal would see Mr Mugabe retaining the presidency and Mr Tsvangirai becoming prime minister with executive powers.
However, there has been no official comment on these reports, apart from statements from all sides that the talks have been progressing well.
Mr Mbeki is under pressure to produce a solid outcome ahead of a mid-August summit of the Southern African Development Community, or Sadc.
Hundreds of thousands of Zimbabweans have fled the country's worsening political and economic situation, many crossing over the borders into neighbouring states of South Africa, Zambia and Botswana.
Botswana's foreign minister suggested on Friday that Mr Mugabe should be barred from the Sadc summit.
"The legal process of producing a government in Zimbabwe has failed [...] those who claim to represent a government in Zimbabwe [...] should be excluded from attending Sadc and African Union meetings as their participation in these meetings would be equal to giving them unqualified legitimacy," Phandu Skelemani said.
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