In the toughest language yet from a state in the region, Botswana’s foreign minister, Phandu Skelemani, called on the 15-nation Southern African Development Community (SADC) to confront Mugabe.
"If no petrol went in for a week, he can’t last," Skelemani told the BBC’s HARDtalk programme, broadcast on Wednesday.
SADC has failed to persuade Mugabe and the opposition to implement an outline power-sharing deal signed in September, widely seen as the best hope for Zimbabwe’s ruined economy.
At new talks that began on Tuesday, Zimbabwe’s opposition vowed to resist any compromise that would leave it sidelined in a unity government with Mugabe’s ZANU-PF party.
Negotiators from ZANU-PF, the opposition Movement for Democratic Change (MDC) and a breakaway MDC faction were hoping to reach a breakthrough in talks with mediator Thabo Mbeki in South Africa on a draft constitutional amendment.
The amendment would allow a new government to be formed under the power-sharing deal with MDC leader Morgan Tsvangirai as prime minister, but the parties are still arguing over the wording and about who should control which ministries.
Skelemani expressed little confidence in mediation, saying SADC should "own up" and admit it had failed, and that it was time for strong action.
Botswana’s president, Ian Khama, has emerged as one of Mugabe’s harshest critics in Africa. Mugabe’s government has accused Khama of interference and said his call for fresh elections was an "act of extreme provocation".
Zambia has also been highly critical of Mugabe.
Skelemani said Botswana would be willing to shelter Morgan Tsvangirai, leader of the main opposition MDC — a position that is likely to anger Mugabe, in power since 1980.
"Anybody who comes to Botswana saying that they fear for their life, from their own country, we would not chase them away because, if we did, what do we want to happen? For them to be killed first? And then do what?" Skelemani said.
In a report issued by his Atlanta-based Carter Center, former U.S. president Jimmy Carter accused Mugabe of refusing to share real power with the opposition and said Zimbabwe might become a failed state if he did not change course.
"Now, after almost three decades of governmental corruption, mismanagement and oppression, Zimbabwe has become a basket case, an embarrassment to the region and a focus of international concern and condemnation," the Nobel laureate said.
"When it is impossible to pay the army and the enormous civil service, the result may be a resort to internecine violence in what could become a failed state, similar to Somalia."
Carter, former U.N. secretary general Kofi Annan and human rights activist Graca Machel, part of a group called the Elders, were barred from entering Zimbabwe last weekend on a humanitarian visit. Mugabe’s government denied them visas, saying the visit was unnecessary.