South African president Thabo Mbeki arrives in Harare Saturday in his role as mediator in the ongoing Zimbabwe political and economic crisis. Peta Thornycroft reports from Harare that although nearly three weeks of hard negotiations between President Robert Mugabe's ZANU-PF and the opposition Movement for Democratic Change have ended, the key issue of executive power is not yet resolved.

Despite many news reports and claims that the secret Zimbabwe negotiations are going well and nearly concluded, the question of executive power still has to be negotiated.

Mr. Mbeki will be in Harare late Saturday and early Sunday to try and conclude this last but most important hurdle.

The MDC's Morgan Tsvangirai easily defeated President Robert Mugabe in the March 29 presidential elections but did not get enough votes to avoid a runoff. He pulled out of the second round because of violence against his supporters. The MDC says more than 120 of its supporters were killed by pro-Mugabe militia in political violence since the disputed elections. Mugabe blames the violence on the opposition. The two sides earlier this week called on their supporters to end violence.

ZANU-PF and MDC negotiators, under heavy international pressure to reach a deal to end Zimbabwe's economic and political crisis, began power-sharing talks two weeks ago mediated by South Africa. But, before a deal can be signed between the two parties, both sides have to decide whether Mr. Mugabe will still hold executive power or whether he will accept a more ceremonial role.

University of Zimbabwe political scientist Eldred Masunungure said Friday that MDC president Morgan Tsvangirai should have executive power because it would reflect the will of the people. He said negotiations over executive power were, what he described "as the heart of the matter."

He also said he believed any decision Mr. Mugabe agreed to would have to be endorsed by the all powerful military.

A ZANU-PF source said that negotiations on executive power would be resolved quickly.

The last stage of the negotiations comes as the economy continues its downward spiral, with an inflation rate of 2.2 million percent.