"Given the Mugabe regime's blatant disregard for the Zimbabwean people's democratic will and human rights, I am instructing the Secretaries of State and Treasury to develop sanctions against this illegitimate Government of Zimbabwe and those who support it," Bush said in a statement.
Residents said they were forced to vote in Friday's poll by threats of violence or arson from Mugabe supporters who searched for anyone without an ink-stained finger - the telltale sign that they had cast a ballot.
"There was a lot of intimidation for people to vote," said Marwick Khumalo, head of the Pan-African Parliament observer mission. "You can tell people just wanted to get the indelible ink to protect themselves from the hooligans."
Contrary to the state-run newspaper's report of a "massive turnout," Khumalo said the turnout was "very, very low." He also said many of those who did vote cast their ballots for opposition leader Morgan Tsvangirai, who pulled out of the race after an onslaught of state-sponsored violence against his Democratic Movement for Change.
Boycotting the poll and spoiling their votes were brave acts by Zimbabweans following the intense violence the opposition faced in the run-up to the election.
Mugabe could try to use the Tsvangirai votes as evidence the election was not a sham, but they are more likely to be seen as a display of the desire to show support for the opposition leader against all odds.
Vote counting continued Saturday, but Zimbabwe Electoral Commission director Shupikai Mashereni said it was "difficult to tell" whether results would be released Saturday or Sunday. Mashereni said he did not know what the hold up was.
Justice Minister and senior ZANU-PF member Patrick Chinamasa said the party was expecting results either Saturday or Sunday.
"From the information filtering in, it looks like a clear win for our president," he said.
An announcement of the result is expected before Mugabe leaves for Monday's African Union summit in Egypt, so he can attend as a victorious re-elected president.
Chinamasa said Mugabe was expected to leave Sunday evening for Egypt, but he would not say whether there were plans for an inauguration beforehand.
"We will have to wait for ZEC," he said referring to the electoral commission.
Zimbabwe refused to allow Western observers to monitor the elections, inviting only "friendly" countries. Khumalo headed an election observer mission that had been reduced from 40 members to 20, while the Southern African Development Community team consisted of about 400 people.
The Herald, Zimbabwe's state-run newspaper, reported Saturday that a massive voter turnout was "a slap in the face for detractors who claimed this was a 'Mugabe election' that did not have the blessing of the generality of Zimbabweans."
Khumalo said the election had been "marred" by a high number of spoiled ballots.
Tsvangirai's name remained on the ballot because his withdrawal on Sunday came too late to remove it, election officials said.
Khumalo said at one voting station in rural Matabeleland, 36 votes were cast for Mugabe, 17 for Tsvangirai and 31 were spoiled. In one Harare voting station, 107 votes were cast for Mugabe, 76 for Tsvangirai and 30 were spoiled, he said.
On Friday, reporters and independent observers in Harare saw low turnout in the capital. As polls closed, officials at one Harare station said they had not seen a voter for several hours.
Marshals led some voters to polls, and militant Mugabe supporters roamed the streets, singing revolutionary songs, heckling people and asking why they were not voting.
Friday's election was widely condemned by African and other world leaders as a sham.
British Prime Minister Gordon Brown on Saturday urged African nations to help bring an end to Mugabe's rule, and called the election a "new low" in Zimbabwe's affairs. The upcoming African Union summit is "an opportunity for the region to restore hope to the people of Zimbabwe. Democracy will ultimately prevail," he said in a statement.
The presidents of Burundi, Kenya, Rwanda, Tanzania and Uganda - in a rare comment about the affairs of another African country - said Zimbabwe's one-candidate runoff, "cannot be a solution," to the country's political crisis.
The presidents, at a regular summit of the East African Community held in Kigali, Rwanda, urged Mugabe's and Tsvangirai's parties "to come together and work out an amicable solution through dialogue in the interest of all Zimbabweans."
Tsvangirai said he still wanted negotiations about a transitional authority for Zimbabwe but was not sure whether he could talk with Mugabe, 84.
Mugabe, who has been president since independence in 1980, offered an olive branch to the opposition Thursday, saying he was "open to discussion" with them.
Tsvangirai was first in a field of four in the March vote, an embarrassment to Mugabe. The official tally said he did not gain the votes necessary to avoid a runoff against Mugabe. Tsvangirai's party and its allies also won control of parliament in March, dislodging Mugabe's party for the first time since independence in 1980.
Mugabe was once hailed as a post-independence leader committed to development and reconciliation. But in recent years, he has been accused of ruining Zimbabwe's economy and holding onto power through fraud and intimidation.
The official inflation rate was put at 165,000 percent by the government in February, but independent estimates put the real figure closer to 4 million percent.
Since the first round of elections, shortages of basic goods have worsened, public services have come to virtual standstill, and power and water outages have continued daily.