JOHANNESBURG, South Africa (CNN) -- Prospects of resolving Zimbabwe's two-week-old election crisis appeared dim after a government spokesman said President Robert Mugabe would not attend a key weekend meeting with other regional leaders.
Opposition supporters say Morgan Tsvangirai won last month's presidential vote.
It is a reversal for Mugabe, who said Thursday he would attend the one-day summit in Lusaka, Zambia sponsored by the 15-member Southern African Development Community (SADC). The SADC called the summit to address Zimbabwe's March 29 presidential vote, the results of which are still unknown.
Mugabe's challenger, opposition leader Morgan Tsvangirai, plans to attend.
Tsvangirai held a face-to-face meeting Thursday evening with South African President Thabo Mbeki in Johannesburg. Details of the meeting were not released, but it comes amid growing pressure on South Africa to step in and help resolve the election.
Tsvangirai's Movement for Democratic Change claims he won the election over Mugabe, but the Zimbabwean government has yet to announce the results.
An MDC spokesman said Thursday that Tsvangirai would not accept a run-off with Mugabe, if one was required, because Tsvangirai won the election.
Tendai Biti had previously said Tsvangirai would participate in a run-off but only under protest.
Without any official results, it is not known whether a presidential run-off is required.
"We will not accept a run-off which is a mere run-off [of] people's rights over people's lives," Biti told a news conference. "That is not acceptable."
The MDC is still hoping Zimbabwe's High Court will find in its favor and compel the Zimbabwe Electoral Commission to release the presidential vote results. The court heard an MDC petition on the matter this week and a ruling is expected Monday. Watch how the political crisis has left ordinary Zimbabweans starving »
Amid the dispute, the MDC and Zimbabwe's national police said Tsvangirai's lawyer was arrested Thursday, though neither was able to say on what charges the lawyer was being held.
Asked Friday why Mugabe decided not to attend the Zambia meeting, a spokesman said: "Why would he go? What would he go as? What could he answer?"
Spokesman Bright Matonga, Zimbabwe's deputy minister of information, said that because Mugabe was a candidate he was -- like everyone else -- powerless to say when the results would be announced or what they would show. E-mail to a friend
CNN's Nkepile Mabuse in Johannesburg and Jim Clancy in Beitbridge, South Africa contributed to this report