The United States says a power-sharing deal in Zimbabwe will not work with Robert Mugabe as president.
As well as an economic collapse, Zimbabwe is suffering from a cholera epidemic.
The opposition MDC party accuses Mr Mugabe of breaking a deal reached on 15 September to form a coalition government and also of abducting its members.
The US had supported the deal - but the Assistant Secretary of State for African Affairs, Jendayi Frazer, says Mr Mugabe is "completely out of touch".
She told reporters in Pretoria that Mr Mugabe was responsible for turning the once prosperous country into a "failed state" where food is scarce and the currency worthless.
Ms Frazer said the US feels he has "has reneged on that deal" and she urged Zimbabwe's neighbours to step up the pressure, saying they were protecting Mr Mugabe by failing to take a tougher diplomatic line.
She said the US will no longer support a government that includes him.