Several thousand Belarussian opposition supporters have gathered in a main square in Minsk as voting in the country's presidential election ended.
They claim that President Alexander Lukashenko has rigged the vote to ensure a third term in office.
Mr Lukashenko has warned he will crush any attempt to stage a popular revolt.
More than two hours before the official end of voting, exit polls on state controlled TV suggested Mr Lukashenko had won 82% of the vote.
The same poll said that the main opposition candidate, Alexander Milinkevich, had won just 5%.
According to election officials the turnout has been more than 80%.
The president has warned he will not tolerate any attempt at a "coup" and has vowed to "break the neck" of anyone who tries to seize power.
Large-scale street protests led to the fall of leaders in other ex-Soviet republics such as Ukraine and Georgia.
Both the European Union and the United States have expressed concern at the Belarussian government's tough stance on political protest.
Police have said that protesters "trying to destabilise the situation" will be treated as terrorists and could face the death penalty.
A spokesman for the Helsinki Committee, a human rights organisation, told the BBC the Belarussian government's threats to opposition groups could trigger violence.
"We've had similar statements during previous elections... This one is stronger and maybe it's a sign that we should expect violence during Sunday evening," Dzmitry Markusheuski said.
Officials in the ex-Soviet republic have accused foreign countries of backing opposition candidates in the election and a number of foreign monitors and journalists have been denied entry to watch the vote.
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Eyewitness: Expelled from Belarus
Eight members of a Scandinavian team of unofficial election observers have been ordered to leave the country, days before the presidential elections.
The BBC News website spoke to one of the those arrested - Michael Johnson, 23, the Belarus co-ordinator for the Social Democratic Youth of Denmark (DSU).
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