PRETORIA, August 12, 2008 (AFP) - Zimbabwe's rival parties should push on with talks even if President Robert Mugabe and the opposition fail to clinch a power-sharing deal this week, South Africa's deputy foreign minister said Tuesday.

'If there is a successful outcome to the talks it will be a plus,' Aziz Pahad told reporters as South African President Thabo Mbeki spent a third day in neighbouring Zimbabwe leading mediation.

'But if no agreement is reached, the parties must be encouraged to continue talking until a solution is found.'

The talks come ahead of a Southern African Development Community (SADC) summit this weekend in South Africa, with Botswana threatening to boycott the gathering of the 14-nation bloc if Mugabe clings to power without a negotiated settlement.

'President Thabo Mbeki is of course expected to give a report to the summit on the mediation process because he has been mandated as the facilitator by SADC,' said Pahad.

Mbeki arrived in Harare late Saturday, with Mugabe, opposition Movement for Democratic Change leader Morgan Tsvangirai and Arthur Mutambara, the head of a smaller MDC faction, holding hours of talks on Sunday and Monday.

A third day of negotiations was set for Tuesday.

Mbeki has been criticised for his quiet diplomacy approach to the country's political and economic crisis.

Mugabe was re-elected in a June run-off poll after Tsvangirai boycotted the vote, despite finishing ahead of Mugabe in the March first round, citing rising violence against his supporters.