Zimbabwean President Robert Mugabe and rival Morgan Tsvangirai were expected to meet this weekend in Harare to work out the final details of a power-sharing arrangement following the conclusion of negotiations this week in Pretoria by negotiators for Mr. Mugabe'slong-ruling  ZANU-PF party and Tsvangirai's Movement for Democratic Change.

South African President Thabo Mbeki was to fly to Harare on Saturday and remain through Sunday to encourage the two leaders to come to a final agreement.

Sources said Mr. Mugabe, Tsvangirai and his fellow opposition leader Arthur Mutambara were to discuss the allocation of powers in a shared government, focusing on the respective roles of Mr. Mugabe and Tsvangirai and on ministerial appointments.

Political sources said there were likely to be two centers of power in the new Zimbabwe with Mr. Mugabe and Tsvangirai sharing executive responsibilities. The arrangement was likened to France's system where a strong president governs alongside a prime minister.

VOA sources said it was not likely a deal would be signed this weekend, but added that the remaining issues are minor, if sensitive. They added that if there is a firm commitment on the part of the leaders the deal can be sealed within hours.

But ZANU-PF sources cautioned that some influential party members backed by the so-called "securocrats" – the heads of the country's security services – don’t like the deal.

South African Foreign Affairs Spokesman Ronnie Mamoepa said the meeting Saturday falls under the mediation process which Mr. Mbeki has been pursuing on behalf of the Southern African Development Community since March 2007.

Political analyst John Makumbe, a University of Zimbabwe professor, told reporter Blessing Zulu of VOA's Studio 7 for Zimbabwe that he believes intense pressure on the principals will oblige them to conclude an accord within days.

Meanwhile, United Nations spokesman Farhan Haq dismissed reports in Harare that U.N. envoy Haile Menkerios is leading a parallel process to the one Mbeki is guiding.

Menkerios, U.N. assistant secretary general for political affairs, was in Pretoria on Friday with officials in Harare withholding approval of his onward travel to Zimbabwe. He had hoped to meet with Mr. Mugabe and Tsvangirai as a member of a high-level reference group formed by the U.N., SADC and the African Union to support the power-sharing talks.

Sources said the U.N. has extended Menkerios’s mission in what observers took as a signal that the global institution is determined to play a role in the Zimbabwe crisis resolution process. Menkerios had been expected to end his trip on Saturday.

U.N. Resident Representative Agostinho Zacharias headed to Pretoria from Harare Friday  to hold emergency consultations with Menkerios.

More reports from VOA's studio 7 for Zimbabwe...