"The authorities in Harare under the present circumstances should not be represented at the political level at any SADC summit as that would be equal to giving them legitimacy."
The statement added: "The ministry of foreign affairs and international co-operation of the Republic of Botswana wishes to announce that his excellency the President Ian Khama will not attend the SADC summit scheduled for August 16 and 17, 2008, in South Africa."
Botswana's foreign minister will represent the country.
Khama's decision not to attend underlines growing pressure from regional leaders on Mugabe and the opposition to agree on sharing power to end post-election turmoil.
Negotiations began last month after Mugabe's unopposed re-election in June, which was condemned around the world and boycotted by Morgan Tsvangirai, the leader of the opposition, because of attacks on his supporters.
Three days of marathon meetings in Harare this week failed to reach an overall deal.
Tsvangirai insisted he needed more time to consider a deal agreed by Mugabe and Arthur Mutambara, the leader of a smaller breakaway opposition faction.
Patrick Chinamasa, the justice minister and spokesman of Zanu-PF, said the talks would resume in South Africa.
"We are travelling to South Africa with President Mugabe today as the negotiations continue," the state-owned Herald newspaper quoted him as saying.
"The talks never collapsed and all parties are committed to the dialogue. I would also want to confirm Zanu-PF's commitment to see the talks end successfully sooner rather than later."
SADC's 14 member states have been involved in a negotiated settlement over Zimbabwe's political crisis with Thabo Mbeki, the South African president, mediating talks between Zanu-PF and Movement for Democratic Change (MDC), led by Tsvangirai.
Tsvangirai arrived in Johannesburg on Friday after his travel documents were briefly seized by the authorities at Harare airport on Thursday.
He was due to address a SADC politics and defence committee.