The trip comes amid rumours that Zimbabwe’s longtime president, 85-year-old Robert Mugabe, was ill.

But Zuma’s spokesman Vincent Magwenya said today that "everything’s on track" for Zuma to meet both Mugabe and opposition leader turned Prime Minister Morgan Tsvangirai.

"There are no concerns because we have not received any official communications on the state of President Mugabe’s health," Magwenya said.

Tsvangirai’s Movement for Democratic Change party accuses Mugabe’s ZANU-PF of stalling on reforms and continuing to attack and harass MDC activists since the coalition was formed in February.

ZANU-PF says the MDC should be pushing harder to get the international community to lift sanctions against Mugabe and his top aides.

Former South African President Thabo Mbeki, who was forced by his African National Congress party to step down shortly before elections in April, advocated quiet diplomacy. Mbeki said pushing Mugabe too hard could backfire, but critics said Mbeki’s approach too often meant appeasing Mugabe.

Zuma, who succeeded Mbeki as both the ANC’s and the nation’s president, "will be more vocal in terms of what we see as deviant behaviour," ANC Secretary General Gwede Mantashe told reporters today.

Mantashe added the harassment of MDC activists was among the issues that "are a hindrance to progress" in Zimbabwe.

He called a recent ZANU-PF walkout from a government meeting over perceived insults to Mugabe "adolescent behaviour."

Both sides in Zimbabwe, Mantashe said, should understand that "you don’t have the luxury of adolescent behaviour. You must be more mature. You must engage each other."

Presidential spokesman Magwenya portrayed Zuma’s planned two-day trip as a fact-finding exercise. Tsvangirai was in Johannesburg earlier this month to present his case.

Now Zuma, Magwenya said, "will get a similar brief from members of ZANU-PF, including President Mugabe."

MDC activists in exile in South Africa, the United States, Britain and Canada presented a memorandum to Zuma today urging him to "unambiguously denounce" ZANU-PF during his visit over political violence and other issues.

"We are willing to go home, to take our skills back to our homeland," said Austin Moyo Sr., chairman of the MDC’s organisation in South Africa. But "we are not sure whether it is quite safe."

Moyo said Zuma should lay out clearly and firmly what Zimbabwe’s neighbours expected, and when they expected it to happen.

"We want more than quiet diplomacy," Moyo told reporters in Johannesburg Wednesday. "It should be constructive criticism, something that will give us milestones."