Kazakhstan's president on Wednesday was officially declared the winner of last weekend's election, while the opposition insisted the vote was manipulated.

President Nursultan Nazarbayev, who has led the oil-rich Central Asian nation since the Soviet era, was re-elected with 91 percent of the vote, according to final results released by the Central Elections Commission. Nazarbayev's closest challenger, Zharmakhan Tuyakbai, received less than 7 percent.

Tuyakbai, leader of the pro-democracy For a Fair Kazakhstan alliance, alleged fraud and called for the election results to be declared invalid. In a statement Wednesday, the alliance accused election authorities of withholding official records of results from some 80 percent of polling stations.

It also complained that election authorities had yet to publish full results with a breakdown for every electoral district, as well as the results of electronic voting that was used in less than 20 percent of the polling stations.

The opposition said the new system, which has not been tested by independent experts, could easily be manipulated, and it had urged voters to use paper ballots.

The alliance also said opposition representatives were not allowed to see the final voter lists at any polling station. It claimed the turnout was not more than 60 percent, as opposed to the official 76 percent figure.

Alikhan Baimenov, leader of the opposition Ak Zhol party who received less than 2 percent of Sunday's vote, said in a statement the official results did not reflect the real outcome of the election.

"They reflect the government's desire to diminish the role of democratic aspirations in society," he said.

The United States said Monday the election did not meet international standards, although some improvements were shown over previous votes.

Observers from the Organization for Security and Cooperation in Europe said opposition supporters had suffered intimidation, beatings and seizure of campaign materials. They also noted pressure on voters and serious violations in counting votes.

Nazarbayev, however, called the election "unprecedentedly democratic."

Kazakhstan, which is four times the size of Texas and borders both Russia and China, has vast oil and gas reserves that are a potential alternative to Middle East petroleum, and its stability matters greatly to the West.

Nazarbayev is credited for the nation's post-Soviet economic progress but is criticized for holding up democratic changes.