South African president Jacob Zuma is due to land in Zimbabwe for a three-day trip, aiming to ease tensions within the fragile power-sharing government.
It is thought Mr Zuma will assess the country's readiness for an election, which could take place next year.
president Robert Mugabe and old rival Morgan Tsvangirai, now prime Minister, united in government a year ago.
But they remain at odds over several key issues and have struggled to turn around Zimbabwe's battered economy.
The crisis in their country has forced some three million Zimbabweans to flee across the border to South Africa, where they live as refugees.
According to South African officials, Mr Zuma is in Harare to facilitate the removal of obstacles which hinder the full implementation of a power-sharing deal.
The BBC's Karen Allen, in Johannesburg, says it seems increasingly likely that his focus will be ensuring that new electoral laws are in place in time for a possible vote next year.
Mr Tsvangirai's Movement for Democratic Change (MDC) wants an election as soon as possible to resolve political disputes with Mr Mugabe's Zanu-pF.
The MDC has accused Mr Mugabe of breaking the power-sharing deal by unilaterally appointing a central bank governor and attorney general.
And the trial of senior MDC politician Roy Bennett on terrorism charges has further divided the two parties.
For his part, Mr Mugabe has angrily criticised Mr Tsvangirai for not doing enough to have Western sanctions lifted.
On a recent visit to the UK, Mr Zuma also tried unsuccessfully to have those sanctions eased.