Mbeki has been mediating between Mugabe's government and the Movement for Democratic Change (MDC), which says he has not been tough enough on the veteran Zimbabwe leader, accused of clamping down on opponents and rigging recent polls to stay in power.

MDC leader Morgan Tsvangirai said Zimbabwe's growing political and economic problems ahead of presidential, parliamentary and council elections on March 29 could overwhelm neighbouring South Africa as it prepared to host the 2010 soccer World Cup.

"We need to see a little courage from Mr Thabo Mbeki ... he can break with his policy of quiet support of the dictatorship in Zimbabwe," Tsvangirai told journalists in South Africa.

"He owes it to our common African humanity, he owes it to his own legacy, he owes it to his own people, he owes it to those (Zimbabweans) who are streaming across the river looking for jobs (and) security in the towns here in South Africa."

"President Mbeki can add his voice to those demanding free and fair elections in Zimbabwe ... without taking risks that we are taking in Zimbabwe ourselves. He won't be arrested ... he won't be teargassed, he won't be charged with treason, and he won't see his supporters being brutalised," Tsvangirai added.

Formed in 1999, the MDC has offered the strongest challenge to Mugabe's 28-year grip on power and says it would have won elections in 2000, 2002 and 2005 if they had not been rigged by the ruling ZANU-PF.

The MDC draws most of its support from urbanites hardest hit by shortages of food, foreign currency, fuel, water and electricity, as well as the world's highest inflation rate of 26,000 percent -- all widely blamed on state mismanagement.

WEAKENED OPPOSITION

But some analysts believe the opposition, already weakened by a split in 2005, could see its urban powerbase whittled away by Simba Makoni, a former finance minister and senior ruling party official expelled from ZANU-PF after choosing to run against Mugabe in the presidential race.

Tsvangirai all but ruled out the prospect of joining forces with Makoni, and insisted his participation in the poll as a likely independent candidate would benefit the opposition.

"We are talking of a political relationship based on fundamental principles here ... Mr Simba Makoni is just as guilty, (having been) part of the ZANU-PF elite which has destroyed our country and that's a fundamental difference."

He dispelled fears that another victory for Mugabe, who has ruled Zimbabwe since independence from Britain in 1980, could trigger the same violence as that which engulfed Kenya after President Mwai Kibaki's contested election win in December.

"The people of Zimbabwe know that conflict, when it degenerates to the level of violence, it is the ordinary person that is going to suffer," Tsvangirai said.

"In Zimbabwe ... desperate as we are, desperate as people are, I think it is something that the people will be discouraged to engage in."

Mugabe denies rigging votes since 2000 and says his party will secure a landslide poll victory next month to silence the MDC and shame Western critics he says are funding his opponents.