South Africa ? Zimbabwe has refused to let Kofi Annan, Jimmy Carter and a South African human rights advocate visit the impoverished country for a humanitarian mission, the three said Saturday.

The former U.N. secretary general, the ex-U.S. president and rights advocate Graca Machel had planned to assess the southern African country’s needs. They are members of The Elders, a group formed by former South African President Nelson Mandela to foster peace and tackle world conflicts.

Annan said no official reason had been given for the refusal, but Zimbabwe’s state-run Herald newspaper reported that the group had been asked to “come at a later date” to accommodate the crop-planting season. It quoted an unnamed source as saying they were seen as antagonistic toward Zimbabwe’s government.

Zimbabweans are suffering from disease and hunger while political crisis over a power-sharing government occupies its politicians. A current cholera outbreak has killed nearly 300 people in Zimbabwe, the United Nations said.

But the three were told Friday night by former South African President Thabo Mbeki, who is mediating the political crisis, that efforts to secure travel visas for the a two-day trip had failed.