South Africa's President Thabo Mbeki says he is "very confident" that mediation will produce a solution for Zimbabwe's political crisis.
President Mbeki has been tasked to seek an end to the Zimbabwe crisis
He was speaking after talks with President Robert Mugabe and opposition officials in the Zimbabwean capital.
There has been a virtual news blackout around the South African-mediated talks but sources suggest they have agreed four of the five points on the agenda.
The sticking point is the last issue - the political climate.
Mr Mbeki stopped off in Harare on his way to the Commonwealth summit in the Ugandan capital, Kampala, to meet both sides.
He told reporters he had visited "to see the president, and the leadership of the MDC [opposition Movement for Democratic Change], so we can reflect on where we are and to report to them as facilitator how the talks have gone."
Mr Mbeki, who has been tasked by the Southern Africa Development Community with helping to find a solution to Zimbabwe's political crisis, said the mediated talks were "going well".
Zimbabwe's opposition leader Morgan Tsvangirai has also gone to Kampala to lobby Commonwealth leaders on the Zimbabwe issue.
MDC leader Mr Tsvangirai also said there had been notable progress.
He said he was confident that the agenda set through the South Africa-led mediation would address the fundamental concerns around elections due next year.
The MDC is lobbying Commonwealth leaders
The BBC's Peter Greste in Johannesburg says the issue of the political climate is proving to be a much harder issue to resolve and the talks are now months behind schedule as a result.
Our correspondent says it encompasses both the violent suppression of the MDC's political activities, and the sanctions that Mr Mugabe's government blames for creating the crisis in the first place.
He says there is no guarantee that President Mbeki will be able to break this deadlock, but at least he will be able to go to the Commonwealth Heads of Government meeting demonstrating real effort, if nothing else.
Zimbabwe withdrew from the Commonwealth in 2003 after it was suspended because of allegations of poll rigging.
But Mr Tsvangirai told reporters in Kampala it was important for the body to continue engaging, to ensure Zimbabwe is rescued from its political and economic crisis.