By Peter Biles
BBC Southern Africa correspondent
South African President Thabo Mbeki is in the Zimbabwean capital, Harare, for mediation talks.
Mr Mugabe welcomed the South African president at the airport
Mr Mbeki is meeting President Robert Mugabe and officials from his Zanu-PF party, as well as opposition leaders.
He has been trying to mediate between the two sides to end Zimbabwe's political and economic crisis and pave the way for free and fair elections.
The signals from South Africa suggest a breakthrough in the negotiations over Zimbabwe's future may not be far off.
After a meeting with President Mbeki on Tuesday, the Irish Prime Minister, Bertie Ahern, said the final aspects could be wrapped up within days.
On Wednesday, South Africa's deputy foreign minister, Aziz Pahad, said it looked as if all substantial issues had been resolved.
Shrouded in secrecy
But there have been sticking points, not least over the timing of presidential and parliamentary elections.
Mr Mugabe says the elections are to be held in March; the opposition Movement for Democratic Change wants them delayed until later in the year.
The MDC is planning a big demonstration next week to demand the introduction of a new constitution before the elections.
President Mbeki's mediation efforts - on behalf of the Southern African Development Community - have been going on for almost a year and have been shrouded in secrecy from the start.
But it is clear that progress needs to be made almost immediately, if the elections are to go ahead in March.