Former U.S. President Jimmy Carter said Saturday that he and others planning a humanitarian mission in Zimbabwe had been refused entry to the impoverished African country.

Carter and two other members of The Elders group — former U.N. Secretary-General Kofi Annan and rights advocate Graca Machel, who is married to Nelson Mandela — had planned to assess the country's humanitarian needs as Zimbabweans are stalked by disease and hunger while political crisis occupies its politicians.

But they 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 group had failed, Carter told reporters at a news conference in Johannesburg.

"We are very disappointed that the government of Zimbabwe would not permit us to come in, would not cooperate," Carter said.

It was the first time the 2002 Nobel Peace laureate has been denied permission to carry out a mission in any country, he said.

Annan, also at the news conference, said no official reason had been given for the refusal. He said they read about it in Zimbabwe's state-run Herald newspaper, which reported Thursday that the group had been asked to "come at a later date" to accommodate the crop planting season. The article also said, however, that the group was seen as antagonistic toward Zimbabwe's government.

Government officials in Harare could not immediately be reached for comment Saturday.

The Elders humanitarian group, formed by Mandela, said the trip was entirely separate from regional attempts to get Zimbabwe's President Robert Mugabe and his rivals to implement a power-sharing agreement stalled since September. The opposition accuses Mugabe, in power since independence from Britain in 1980 and seen as increasingly autocratic, of trying to hold onto the most powerful Cabinet posts.

The political impasse has left Zimbabwe without leadership as its economy collapses. The consequences are deadly — lack of cash to buy spare parts for and maintain water and sewer systems, for example, has led to a cholera outbreak in Harare, where the disease had until recent years not been a killer.

The World Health Organization said Friday that 294 people had died in a cholera outbreak.

"It seems obvious to me that the leaders of the government are immune to reaching out for help for their own people," Carter said.

The group members said they would continue efforts to address the humanitarian crisis in Zimbabwe and planned to meet various organizations in South Africa.

Machel said she was denied a visa in July when she had planned to lead a women's delegation to Zimbabwe.