Mugabe's comments followed those of U.S. Assistant Secretary of State for African Affairs Jendayi Frazer's statements that a September power-sharing deal in Zimbabwe would not work with Mugabe in his current position.
Frazer also said the United States would not drop its sanctions while Mugabe was in power. Mugabe has faced intensifying criticism from abroad over the growing humanitarian crisis in his country, which includes a cholera outbreak exacerbated by poverty and a crumbling health system.
Mugabe replied that criticism from President Bush was irrelevant and the "last kicks of a dying horse," quoted the BBC.
"Let him keep his comments to himself. They are undeserved, irrelevant, quite stupid and foolish," he said.
The British government backed the U.S. position on Monday, with U.K. Africa Minister Mark Malloch Brown saying Mugabe was incapable of following through on a power-sharing arrangement with the opposition.
"Power-sharing isn't dead but Mugabe has become an absolute impossible obstacle to achieving it," Malloch Brown said, the Associated Press reported.
Mugabe has ruled the country since it gained independence from Britain in 1980, and has refused to step down following disputed elections in March.
Britain and the United States have been urging African governments, especially those in southern Africa, to take action against Mugabe, but African leaders are wary of being seen as simply following the Western lead.
"The only likelihood is that they (African leaders) will harden their stance against so-called Western imperialism," said John Makumbe, a political science professor in Zimbabwe, according to the AP. "I think (Mugabe) actually enjoys all that pressure and sees it as giving him the limelight."
Meanwhile, Bloomberg News reported that Mugabe is planning to take over key businesses in banking, mining and manufacturing, according to two members of his ruling party who spoke on condition of anonymity.
Mugabe has said he may form an economic revolutionary council to counteract sanctions, the officials said.