Johannesburg - Zimbabwe's political rivals were due to hold talks in South Africa on Tuesday to try to resolve their months-long standoff over the formation of a unity government, but it was unclear whether the opposition Movement for Democratic Change (MDC) would participate.

MDC leader Morgan Tsvangirai was meeting Tuesday morning with senior members of his party in Johannesburg to discuss their stance on the planned meeting with representatives of President Robert Mugabe's Zanu-PF.

The party is concerned that the agenda of the meeting to be chaired by former South African president and mediator in Zimbabwe, Thabo Mbeki, is too narrow and wants it expanded to include all of its concerns.

MDC spokesman Nelson Chamisa would only say from Harare: "Our team headed by our secretary general Tendai Biti left Zimbabwe for South Africa with a view to stating our case and concerns."

Zanu-PF and two factions of the MDC, the biggest one led by Tsvangirai and a breakaway faction led by scientist Arthur Mutambara, were due to hash over the wording of a constitutional amendment that will set out Tsvangirai's powers as prime minister.

The September 15 deal signed by Mugabe, Tsvangirai and Mutambara before the world's cameras made Tsvangirai prime minister of a unity government of 31 ministries while Mugabe remains president.

But the deal was sketchy on how executive power, including the right to hire and fire ministers and senior officials, would be divided between the two leaders.

Because the position of prime minister was scrapped in the 1987 and replaced with that of executive president, the constitution has to be amended to resurrect it.

Zimbabwe's government and the regional Southern African Development Community (SADC) are presenting the amendment as the only hurdle to cleared before a government can be formed.

But there are several other sticking points impeding the implementation of the September deal.

The MDC is demanding, among other things, an equitable distribution of cabinet portfolios between Zanu-PF and the MDC.

The current government proposal, backed by SADC, is heavily skewed in Zanu-PF's favour, giving it control of nearly all the key ministries, bar finance, despite the MDC being the biggest party in parliament.

Zanu-PF would also retain control of the army and share control with the MDC of the justice ministry, which controls the police, in a "co-ministering" arrangement that the MDC rejects.

The two sides are under pressure to agree a deal to rescue the country from a worsening humanitarian crisis.

A cholera outbreak that has claimed nearly 300 lives had compounded the misery of Zimbabweans, over a quarter of whom already require food aid.

On Monday, former US president Jimmy Carter, one of three members of The Elders grouping of leading activists and ex-world leaders that has been assessing the situation, said "the crisis in Zimbabwe is much worse than anything we had ever imagined". (dpa)