"The inclusive government does not include Mr Bush and his administration. It doesn't even know him," Mugabe said in a speech at a funeral ceremony for an official from his ruling Zanu-PF party.
"It has no relationship with him, so let him keep his comments, they are undesired, irrelevant, quite stupid and foolish," he said.
"We realise these are the last kicks of a dying horse. We obviously are not going to pay attention."
Mugabe and Morgan Tsvangirai, the head of the opposition Movement for Democratic Change (MDC), agreed in September to form a unity government, a pact supported at the time by the United States.
But that agreement, which would have left Mugabe as president and made Tsvangirai prime minister, has unravelled due to a fight over control of important ministries.
Mugabe says that new elections could be held "in the next one-and-a-half to two years" if an agreement on power-sharing between the ruling Zanu-PF party and the MDC cannot be reached.
Mugabe 'out of touch'
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| The White House says Mugabe is to blame for ruining Zimbabwe [EPA] |
On Sunday Jendayi Frazer, the US assistant secretary of state for African affairs, accused Mugabe of reneging on the power-sharing pact, saying he was "completely out of touch". She also said he was responsbile for turning the once prosperous country into a "failed state".
But despite mounting criticism of his rule, there is little that Western powers can do to force Mugabe out.
Sanctions have failed to weaken him and analysts say that military intervention in unlikely because Zimbabwe is not seen as a strategic country with key resources such as oil.
But South Africa, the leading diplomatic power in the region, said on Sunday that keeping Mugabe as president, while giving Tsvangirai an office as prime minister, is the only solution to Zimbabwe's political crisis.
While the stalemate drags on, Zimbabwe continues to sink deeper into crisis and leaving millions of Zimbabweans to struggle for basic survival.
Hyper-inflation means prices double every day, a cholera epidemic has killed more than 1,100 people and the opposition has accused the ruling party of abducting its supporters, a charge it denies.