The United States has been pushing African states, particularly the 15-nation Southern African Development Community, to take firmer action on Zimbabwe, where the economy and infrastructure have collapsed, spawning food shortages and a cholera epidemic that has killed nearly 800 people so far.
Zimbabwe’s neighbors are divided over what approach to take, with Mugabe still viewed by many as a hero for liberating the country from white minority rule. This week the African Union rejected tougher action in favor of more dialogue.
"There is a continued outcry from African nations that this is an African problem and it needs an African solution. But so far they have been unwilling to step up and show us what that African solution is," the senior U.S. official said, speaking on condition of anonymity.
"That African solution is very simple — get rid of Mugabe."
Once hailed as a model African democrat, Mugabe has clung to power for years, despite the worsening economic crisis that critics blame on his policies. After losing parliamentary elections in March, he reached a power sharing deal with the opposition, but talks on implementing it have stalled.
The U.S. official said a popular uprising to oust Mugabe was unlikely as the "real risk-takers" had already fled to neighboring countries to seek work there.
"Somebody from the outside is going to have do this. … At the end of the day South Africa," he said, referring to the continent’s biggest power which has borne the brunt of Zimbabwe’s refugee crisis.
"It takes something as simple as closing the borders. Zimbabwe is a landlocked country. The closure of the border, literally in a week would bring this country to its knees," he said.
"There is still a formal economy in Zimbabwe — $2 billion still flows into this country through various means, and even a lot more in the informal economy. A lot of that money flows across the borders, illegally or legally, with South Africa."
He said the U.S. government, which has urged Mugabe to step down, was working behind the scenes with South Africa "to do what they think is in their best interests." South Africa has so far favored dialogue over confrontation with Mugabe.
South Africa declared a stretch of its border with Zimbabwe a disaster zone on Thursday because of the increase in cholera cases but did not appear to have sealed it.
State Department spokesman Sean McCormack said on Thursday he expected Secretary of State Condoleezza Rice, who has urged Mugabe to step down, to raise the Zimbabwean crisis with her colleagues during a visit to the United Nations next week.
At a separate news conference in Washington, the U.S. ambassador to Zimbabwe, James McGee, said Zimbabwe was rapidly becoming a failed state. He also blamed the cholera crisis on the government’s mismanagement, saying it was "man-made."
At the same briefing, Henrietta Fore, the administrator of the United States aid agency USAID, said the epidemic was worsening, contradicting Mugabe’s assertion in a televised speech earlier in the day that it had been contained.
She said USAID was providing an additional $6.2 million toward health, water and sanitation programs and had deployed. This was on top of the $4.6 million it was already spending.
Another USAID official, Ky Luu, said the agency was bracing for the epidemic to spread with the onset of summer rains, which would contaminate wells, and the annual Christmas migration of urban residents to their rural family homes.