Johannesburg, South Africa — Zimbabwe faces the possibility of a military coup or civil war if negotiations between President Mugabe and the democratic opposition fail, Botswana’s foreign minister has warned.

As heads of state from Zimbabwe’s neighbors gathered in Johannesburg for a regional summit, Botswana’s new president, Ian Khama, boycotted the meeting in protest at the presence of Mr. Mugabe, who he regards as illegitimate after he was “re-elected” in a one-candidate presidential run-off.

While the octogenarian leader sat on the podium nodding his head in time to a military band playing “When the saints go marching in,” the front-row seats of the Botswana delegation in the hall were conspicuously empty.

Talks between Mr. Mugabe and Morgan Tsvangirai, leader of the Movement for Democratic Change, and Arthur Mutambara, who heads another MDC faction, continued during the gathering, but without reaching a resolution.

Botswana’s foreign minister, Phandu Skelemani, said a successful outcome to the negotiations was crucial.

“If they fail the situation will spiral,” he said. “There’s going to be turmoil. Then we are really heading for trouble. Some mad chap might think ‘these fellows have failed, now I’m taking over.’ Those are the risks you run.

“I’m not sure that the Zimbabweans are not going to start fighting, then we are all in trouble. There’s no option but to agree. The consequences are too ghastly to contemplate.”

President Mbeki of South Africa, mediating the talks, claimed that the negotiations could be finalized during the summit. But Mr. Tsvangirai’s secretary-general and chief negotiator, Tendai Biti, retorted: “He’s dreaming.”

The negotiations are understood to be stymied over the question of executive authority, with Mr. Mugabe insisting on remaining as head of the government, leaving the effective power of Mr. Tsvangirai’s proposed prime ministership open to question.

In a speech to ministers, Mr. Tsvangirai said: “We have agreed that Mr. Mugabe will be president whilst I become prime minister. A prime minister cannot be given responsibility without authority and be expected to deliver.

“We envisage that the prime minister must chair the Cabinet and be responsible for the formulation, execution, and administration of government business including appointing and dismissing his ministers.”

On the summit sidelines he added: “No deal in the short-term is better than a bad deal.”

Botswana’s foreign minister, Phandu Skelemani, said his country faces a “very serious” situation as a result of Zimbabwe’s impoverishment, with economic refugees “streaming across” their shared border at an increasing rate.

In a clear reference to the man who has led Zimbabwe since independence 28 years ago, he said: “Over the years the political situation may have been bad, the crunch has now come.

“The country is melting economically, I don’t think Mr. Mugabe can fail to see that. If he sees that and being the patriot that I believe he is he must have only one answer, that the Zimbabweans look up to him and the other leaders of the political parties to find a resolution.”