TEGUCIGALPA, Honduras—The opposition presidential candidate in last week's elections in Honduras is citing allegedly altered tally sheets, ballots cast by dead or absent people, and inadequate monitoring of polling stations in her bid to have a recount of a vote she calls fraudulent.

Xiomara Castro's call for her supporters to pour out in the streets to demand a vote-by-vote recount of last Sunday's election threatens further political instability for this poor Central American country. Castro's husband, former President Manuel Zelaya, was ousted in a 2009 coup that left the country polarized.

Honduras' electoral court has declared conservative Juan Orlando Hernandez, of the ruling National Party, the election winner. The court says he received 37 percent of the votes compared to 29 percent for Castro, with 96 percent of the votes counted. Six other candidates shared the remaining votes.

Voting was monitored by missions from the European Union and Organization of American States, which concluded that the election process was transparent despite irregularities including a faulty system for issuing poll workers' credentials and electoral lists in which people who are either dead or who left Honduras long ago could account for up to 30 percent of registered voters.

"Transparency does not guarantee that there are no mistakes in the process," said Jose Antonio de Gabriel, deputy chief of the European Union's observer mission. "But we do see the Electoral Tribunal has the will to correct them."

But Castro, 54, and her leftist Libre party say that the irregularities go beyond mistakes and amount to election fraud.

Late Friday, Castro called the election "a disgusting monstrosity that has robbed me of the presidency" and said she will not recognize Hernandez's government. She called for a street protest on Sunday.

Ricci Moncada, Libre's representative on the Electoral Tribunal, said that many vote tally sheets were altered and in some cases falsified by including the votes of people no longer in Honduras to benefit Hernandez, adding that this was possible because there wasn't fair oversight at many voting stations.

In Honduras, the Supreme Electoral Tribunal issues the country's eight political parties credentials to have their members working polls on election day to avoid fraud. But the credentials only include the name of the party and location of the poll.

Castro accused some of the smaller parties of selling their spots at polling stations to members of Hernandez's National Party.

Castro is not the only candidate who rejects the result.

The Anti-Corruption Party candidate, Salvador Nasralla, who won almost 14 percent of the vote, has officially filed a complaint challenging the results.

Asked about the fraud allegations, electoral tribunal president David Matamoros said the vote tally sheets have been closely reviewed.

"We must check to leave no doubt that the counts are correct," he said.

Hernandez has said his victory is legitimate and that he won't negotiate. But he hasn't comment directly on the fraud allegations.

The elections also left a divided Congress.

The National and Liberal parties had long split the majority of the legislative seats, but the recent creation of the Libre and Anti-Corruption parties has changed that.

Last week's voting to replace 128 lawmakers left the National Party with 48 seats, Libre with 39, the Liberal Party with 25 and the Anti-Corruption Party with 13.