President Ian Khama of Botswana has called for Zimbabwe's contested presidential election to be re-run under international supervision.

Delivering his state of the nation address to the Botswana Parliament ahead of this weekend's planned summit of Southern African leaders, Khama said member states of the Southern African Development Community (SADC) had to uphold the regional standards of governance they had adopted.

Botswana was seriously concerned about Zimbabwe's "failure to form a Government that is widely accepted by the people of that country," Khama said. "The one viable way forward" was to re-run the presidential election.

"That way a repeat of the past run-off presidential election, which was declared by regional and international observers to be neither free nor fair and was characterised by intimidation and violence, can be avoided," he added. "It should be unacceptable for ruling parties to seek to manipulate election outcomes to extend their stay in power, as this is bad for democracy on our continent."

The South African foreign ministry has told news agencies that a SADC heads of state summit has been called for Sunday to discuss the deadlock over the formation of a power-sharing government in Zimbabwe and the violence in the eastern Democratic Republic of Congo. South Africa currently chairs SADC.

Movement for Democratic Change leader Morgan Tsvangirai beat President Robert Mugabe in the first round of this year's presidential election in March, but not by a big enough margin to avoid a run-off. Tsvangirai pulled out of a June run-off in protest at the violence perpetrated on his supporters ahead of polling.