"We are deeply saddened that after eight years of mediation, all the talks have borne no fruit," the conference said in a statement.
It said Mugabe was "clearly willing" to watch his people die of starvation and cholera, as long as he was able to retain his 28-year-old hold on power.
"The South African government has the capacity to force Mugabe to go. All that is lacking is the political will.
"We are extremely disappointed at the inability of the SADC [Southern African Development Community] leadership, including the new South African president [Kgalema Motlanthe], to make any headway."
Motlanthe this week refused to join growing international calls for Mugabe to go, saying he hoped a deal on a unity government in Zimbabwe could be implemented within days.
Mugabe’s regime and the opposition Movement for Democracy and Change, which won the most votes in March elections, agreed to a power-sharing deal in September, but remain locked in dispute over the control of key ministries.
According to the latest UN figures, the cholera epidemic in Zimbabwe has claimed more than 1 000 lives. – SAPA