Botswana's president will boycott a summit of regional leaders in South Africa because Zimbabwe's leader, Robert Mugabe, has been invited.
In what's described as an unprecedented move, Botswana is urging the Southern African Development Community not to give legitimacy to the second round of Zimbabwe's presidential election.
A statement issued by the goverment says the run-off election on 27 June violated the core principles of SADC, the African Union and the United Nations.
Mr Mugabe was the only candidate in the poll.
Botswana says he should not attend SADC gatherings until a power-sharing deal is reached in Zimbabwe.
The stance is the toughest taken by Zimbabwe's neighbours.