"We call for an end to the Mugabe regime’s brutal repression of basic freedoms and for the formation of a legitimate government that represents the will of the people as expressed in the March 2008 elections," Bush said in a statement released as he attended an Asia-Pacific summit in Peru.
Opposition leader Morgan Tsvangirai of the Movement for Democratic Change won the most votes in March’s presidential election but fell short of an outright majority.
He pulled out of a run-off against Mugabe, who has ruled Zimbabwe non-stop since independence from Britain in 1980, accusing the 84-year-old of orchestrating attacks against his opposition supporters.
"Nearly eight months have passed since the Zimbabwean people voted for a new president, yet they still are governed by an illegitimate regime that continues to suppress democratic voices and basic human rights," said Bush.
"In addition to its disastrous economic policies which have forced half the population to rely on food assistance, the Mugabe regime is now assaulting doctors and nurses, denying citizens access to basic medical services, and stealing donor funds intended for HIV/Aids patients," he charged.
1 300 incidents
Bush said that, in October alone, independent organizations had documented about 1 300 incidents of politically motivated violence and harassment by the regime.
Washington will honour its pledges of emergency humanitarian aid, which totalled 186 million dollars in 2008, and "stands ready to provide other forms of assistance pending the formation of a legitimate government that represents the will of the Zimbabwean people," he vowed.
Power-sharing talks between Mugabe and Tsvangirai have yet to yield a unity government, despite several failed attempts by regional leaders to force the implementation of a September 15 accord.
Zimbabwe’s economy has been in free-fall for years, leaving 80% of the population in poverty and nearly half the country in need of emergency food aid by January, according to the United Nations.
The country suffers the world’s highest inflation rate, last estimated at 231 million percent in July, causing a breakdown in water and sanitation that has sparked an outbreak of cholera that has killed 294 people in recent weeks, according to the US ambassador.
Western nations have said they are ready to release hundreds of millions of dollars in aid, but not while Mugabe retains his sole grip on power.