JOHANNESBURG, South Africa (CNN) -- Zimbabwe opposition leader Morgan Tsvangirai will announce on Saturday whether he will take part in a presidential runoff, a spokesman for his party said Friday.
South African President Thabo Mbeki, left, with Zimbabwe leader Robert Mugabe at Harare airport on May 9.
The Movement for Democratic Change spokesman in Johannesburg said Tsvangirai would make the announcement at 0900 GMT (4 a.m. ET) in the South African capital of Pretoria.
Zimbabwe's electoral commission announced last week that Tsvangirai won more votes than incumbent Robert Mugabe in the March 29 presidential race, but not enough to avoid a runoff.
The commission has yet to announce a date for the runoff, and Tsvangirai had previously insisted he would not announce his decision until that date was set.
The MDC promised last week that Tsvangirai would announce his decision over the weekend, only to say Sunday he needed more time for consultation.
The party has refused to agree to a second round of voting, claiming Tsvangirai already has enough votes to replace Mugabe.
The MDC said the initial tally of votes showed Tsvangirai garnered 50.3 percent, which would have averted a runoff. The electoral commission's official tally showed Tsvangirai won 47.9 percent compared with 43.2 percent for Mugabe.
If Tsvangirai refuses to support a runoff, Mugabe will remain president.
Meanwhile, South African president Thabo Mbeki arrived in the Zimbabwe capital, Harare, Friday for more election crisis talks with the political leadership there, the South African Foreign Affairs Ministry said.
A ministry statement said only that Mbeki would be traveling in his capacity as head of the Southern African Development Community (SADC), which represents a dozen regional countries.
Mbeki was likely to discuss a continuing crackdown by the Zimbabwean government on dissenting voices in the aftermath of the unresolved March 29 presidential election.
Mbeki dispatched a team earlier this week to look in to the violence in neighboring Zimbabwe. Mbeki's office did not give any details.
The opposition party has said 25 of its supporters have been killed since the vote, and this week, police arrested two journalists, a lawyer and a trade unionist.
Mbeki has sided with Mugabe on the election issue, saying it was not a crisis at their last meeting in Harare on April 12.
However, Tsvangirai has been critical of Mbeki's mediation role in Zimbabwe, calling for him to step aside.
The MDC leader said problems in Zimbabwe began long before the recent election and that Mbeki had been part of the mediation discussion for close to a decade.
"Well, it is nine years since the emergence of this Zimbabwean crisis. In any measure of success, I think nine years is too far, too long without a resolution in sight," Tsvangirai said.
"So I think that those who are making this criticism of the role played by President Mbeki, I think, are justified," he told CNN.
The Zimbabwean government's crackdown on dissenting voices appeared no closer to an end Thursday, with two journalists, a lawyer and a trade unionist among those arrested for varying alleged offenses in the past few days.
One of those arrested, a Zimbabwean photographer for Reuters, was released on bail Thursday after three days in jail, the news agency said.
Police accused Howard Burditt of using a satellite phone to transmit pictures, Reuters said. Burditt, who was covering the aftermath of the elections, has accreditation to work in the country, the agency said.
Davison Maruziva, the editor of the privately owned paper The Sunday Standard, was arrested Thursday for allegedly "publishing falsehoods."
Raphael Khumalo, the chief executive of the paper, said Maruziva was arrested over an opinion piece that appeared in his paper April 18 by student activist-turned-opposition-politician Arthur Mutambara.
CNN's Nkepile Mabuse contributed to this report.