Independent observers said Monday the re-election of iron-fisted President Alexander Lukashenko was "a farce" because his opponents were systematically intimidated and detained.
The United States called for new elections in Belarus, with the White House and European Union also hinting at sanctions against Lukashenko's authoritarian government.
"The United States does not accept the results of the election," White House spokesman Scott McClellan said.
However, Russia hailed the election held by its ally and said the result that gave Lukashenko a third term "must be viewed with respect."
Official results showed Lukashenko with 82.6 percent of the vote, Central Election Commission chief Lidiya Yermoshina said. Main opposition candidate Alexander Milinkevich received 6 percent, she said, citing a complete preliminary ballot count.
Underlying the election is a struggle for regional influence between Russia and the West, which is seen by Lukashenko's government and its backers in Moscow as a major culprit in the political upheaval in former Soviet republics of Ukraine, Georgia and Kyrgyzstan.
About 10,000 people demonstrators turned out at a peaceful anti-government protest Sunday night in Minsk's Oktyabrskaya Square, signaling a bid to gather growing street rallies like those that brought opposition leaders to power in neighboring Ukraine.
Milinkevich and the other opposition candidate, Alexander Kozulin, called for larger crowds to turn out Monday evening. Busloads of riot police in helmets and camoufalge uniforms streamed into the capital, went into neighborhood courtyards, and prevented pedestrians from walking toward the central square.
At a boastful and belligerent nationally televised news conference where he repeatedly criticized the United States, Lukashenko repeated allegations that the opposition was backed by Western forces plotting to bring him down.
"The revolution that was talked about so much ... has failed," he said, adding that Belarusians had resisted "colossal pressure from outside" and "showed who's the boss."
"You have seen our opposition, and if you are reasonable people you have been convinced that it's worthless," said the 51-year-old leader who has ruled since 1994.
Monitors from the Organization for Security and Cooperation in Europe and the Council of Europe said the election was neither free nor fair.
"The March 19 presidential election did not meet the required international standards for free and fair elections," said Rep. Alcee Hastings, D-Fla., who chairs the OSCE parliamentary assembly, the world's largest regional security organization.
The mission said "arbitrary use of state power and widespread detentions showed a disregard for the basic rights of freedom of assembly, association and expression, and raise doubts regarding the authorities' willingness to tolerate political competition."
The European Union said the elections were marred by intimidation, and the 25-nation bloc likely will impose financial and diplomatic sanctions on Belarus' top political leaders. McClellan also said penalties such as travel restrictions "are things we will look at."
Austrian Foreign Minister Ursula Plassnik, whose country holds the EU's rotating presidency, said the opposition "was systematically intimidated" during the campaign.
She said preparations for the election "were conducted in a climate of intimidation, a climate of hindering" Lukashenko opponents.
"In a country in which freedom of expression and association are so thoroughly and aggressively suppressed, a vote is not an exercise in democracy, it is a farce," said Terry Davis, president of the Council of Europe, the continent's premier human rights organization.
EU External Relations Commissioner Benita Ferrero-Waldner said "some action is now very likely," including a visa travel ban on top government leaders in Minsk. EU foreign ministers also are considering expanding a freeze on the assets of top Belarus officials, Ferrero-Waldner said.
Milinkevich called the official vote tally for Lukashenko "monstrously inflated" and denounced the leader as an "illegal, illegitimate president."
"In Belarus, we did not have an election but an unconstitutional seizure of power," he said, repeating his demand for a revote "in which he law of the country is followed."
The Soviet past is strongly palpable in Belarus. The government makes five-year plans, the main state newspaper has "Soviet" in its title and the state security service is still officially called the KGB. Russia, which has an agreement with Belarus envisaging close political, economic and military ties, has staunchly backed Lukashenko, who has become a pariah in the West for his relentless crackdown on opposition and independent media.
Western countries have forged close ties with the opposition and made no secret of their contempt for the ruler of what Washington calls an outpost of tyranny in Europe. The United States condemned the election campaign as "seriously flawed and tainted."
After polls closed Sunday, thousands of opposition supporters jammed Oktyabrskaya Square, shouting, "Freedom!" and "Long live Belarus!" in scenes reminiscent of protests that brought opposition leaders to power in other former republics.
Demonstrators waved a national flag that Lukashenko scrapped in favor of a Soviet-style replacement, as well as European Union flags.
People blew horns and chanted "Mi-lin-ke-vich!" — echoing the much larger crowds on Kiev's Independence Square in Ukraine's 2004 Orange Revolution, which turned the nation toward the West.
Lukashenko had vowed to prevent mass rallies. The use or threat of force neutralized opposition efforts to protest vote results in Azerbaijan and Kazakhstan last year, and a bloody government crackdown in Uzbekistan left hundreds dead.
The authorities made no move to disperse Sunday's protesters, but busloads of riot police idling on a nearby street were a reminder of the government's threats of a decisive response.
Lukashenko said the protest leaders were in the pay of Western ambassadors and said there was no crackdown because the opposition is weak.
"Who was there to fight with? Nobody, understand? That's why we gave them the opportunity to show themselves, even though it was illegal," he said.
The crowd was the biggest the opposition had mustered in years, reaching at least 10,000, according to reporters' estimates. After about three hours, a smaller group marched to nearby Victory Square, some laying carnations at a monument before dispersing around midnight.
But Milinkevich's campaign chief, Sergei Kalyakin, said Sunday's protest was not big enough, and that crowds 10 times larger were needed to force the authorities "to hear the voice of the people."
While Lukashenko is a dictator to his opponents and foreign critics, many Belarusians see the former collective farm manager as having brought stability after the uncertainty that followed the 1991 Soviet collapse. While the landlocked nation, about as big and flat as Kansas, is far from prosperous, the economy is growing and salaries are rising.
Critics say the economic successes are unsustainable, based largely on cheap Russian energy and heavy-handed state intervention reminiscent of the communist era.