Belarus on Monday detained over 600 protestors, including seven opposition candidates, after smashing a mass rally protesting fraud in the landslide re-election of President Alexander Lukashenko.
Western governments were quick to condemn the vote and the crackdown, with the United States saying it did not consider the election results legitimate.
Lukashenko, described as Europe's last dictator by Washington, won Sunday's polls outright with 79.6 percent of the vote on the back of a massive voter turnout of over 90 percent, the central election commission said.
His nearest rival received less than three percent in polls which the OSCE observer mission said showed the ex-Soviet state was still a "considerable way" from holding democratic elections, noting a flawed vote count.
Tens of thousands of outraged voters had braved arrest to gather in central Minsk overnight, some trying to storm government buildings and smashing glass doors.
But a reinforced contingent of anti-riot police arrived, encircling the protestors and taking hundreds into waiting police vans. AFP correspondents saw several protestors beaten with truncheons.
Apparently showing no qualms about the mass arrests, Lukashenko announced at a news conference that 639 protestors were being held in Minsk detention facilities.
"What was attempted yesterday in Minsk is banditry. These are vandals," Lukashenko told reporters. "There is not going to be a revolution in Belarus."
In what appeared to be a massive government crackdown on the opposition, seven of the nine challengers to Lukashenko were also arrested by Monday morning, their representatives told AFP.
State Department spokesman Philip Crowley said Washington agreed with the OSCE's assessment of the election.
"We cannot consider the election results yesterday as legitimate," Crowley said.
At the White House, President Barack Obama's spokesman Robert Gibbs also said the poll could not be seen as legitimate and condemned the crackdown.
"The United States strongly condemns the actions that the government of Belarus has taken to undermine the democratic process and (the use of) disproportionate force against political activists, civil society representatives and journalists," said Gibbs in a written statement.
"We call for the immediate release of all presidential candidates and the hundreds of protestors who were detained on December 19 and 20."
EU chief diplomat Catherine Ashton condemned the use of violence and urged the immediate release of those detained.
Russian President Dmitry Medvedev, who has had a prickly relationship with Lukashenko, however showed no sign of wanting to intervene over the police action, saying the election "is an internal matter for Belarus".
The Organization for Security and Cooperation in Europe (OSCE) observer mission said that while the voting itself was smooth, the process deteriorated significantly during the count.
"Observers assessed the vote count as bad and very bad in almost half of all observed polling stations. The count was largely conducted in a non-transparent manner, generally in silence, which undermined its credibility," it said.
Authorities opened a criminal investigation into the violence, with some of those rounded up facing up to 15 years in prison for "organising mass disturbances".
About 30 young people who gathered to protest late Monday were also attacked and detained by police, witnesses told AFP.
The events were reminiscent of the police response to the last vote in 2006, when mass demonstrations were forcefully broken up and opposition leaders sentenced to jail.
An AFP journalist was also arrested during the crackdown and released Monday with no explanation after spending the night in detention.
Lukashenko, who has ruled the former Soviet republic of 10 million for the past 16 years, has in recent months sought to move Minsk away from Russia's orbit, repeatedly sniping at Moscow, which shot back with a muck-raking television documentary on him called "The Godfather".
He has also sought closer ties with the European Union and eased controls on the opposition during the campaign, a move that had appeared aimed at impressing international election observers.