PRETORIA, South Africa - The United States can no longer support a proposed Zimbabwean power-sharing deal that would leave Robert Mugabe, "a man who's lost it," as president, the top U.S. envoy for Africa said yesterday.

Jendayi Frazer, the U.S. assistant secretary of state for African affairs, made the announcement in South Africa after spending the last several days explaining the U.S. shift to regional leaders. The new U.S. stance will put pressure on Zimbabwe's neighbors - South Africa in particular - to abandon Mugabe. But South Africa said its position was unchanged.

The United States, Frazer said, has become convinced that Mugabe is incapable of sharing power.

She cited political moves he has made since September without consulting the opposition, reports his regime has continued to harass and arrest opposition and human-rights activists, and the continued deterioration of Zimbabwe's humanitarian and economic situation. Particularly worrying, she said, was the rapid spread of cholera, an easily treatable and preventable disease that has killed at least 1,000 Zimbabweans since August.

Frazer cited accusations from the Mugabe regime that the West waged biological warfare to deliberately start the cholera epidemic as an indication that Mugabe is "a man who's lost it, who's losing his mind, who's out of touch with reality."

If Mugabe's neighbors were to unite and "go to Mugabe and tell him to go, I do think he would go," she said.

Secretary of State Condoleezza Rice said yesterday on NBC's

Meet the Press

that Zimbabwe was discussed at the United Nations last week.

"This is another circumstance in which the international community, most of it - including, by the way, several African states: Botswana, the leadership of Kenya and others - are saying that the regime of Robert Mugabe has got to go," Rice said. "You have a cholera epidemic there. You have a humanitarian disaster in terms of food. You have the goons of the Mugabe regime going around and detaining people and frightening people, terrorizing people. Again, the international community in that circumstance needs to act."

But South Africa said yesterday that the agreement under which Mugabe would remain president and opposition leader Morgan Tsvangirai would take a new prime minister's post was the only way forward.

South Africa is the region's diplomatic leader. Its former president, Thabo Mbeki, mediated Zimbabwe's power-sharing agreement in September and has worked since then to break an impasse between Mugabe and the Zimbabwean opposition over how to divide cabinet posts.