The Belarussian opposition has called for a mass rally after polls close in Sunday's presidential election, to protest at alleged ballot-rigging.
A pro-Lukashenko poster in Minsk reads "For Belarus! For Plenty"
Chief opposition candidate Alexander Milinkevich predicted that fraud would return President Alexander Lukashenko to office with 70% of the vote.
Mr Lukashenko has warned he will not tolerate any attempt at a "coup".
Police have said that protesters "trying to destabilise the situation" will be treated as terrorists.
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.
Mr Lukashenko, a close ally of Russia, is running for his third term in office and points to economic growth and social stability as his main achievements.
Opinion polls were rare during the election campaign but those taken suggested Mr Lukashenko would win the first round.
Holding his final campaign meeting on Saturday, Mr Milinkevich told an audience of a few hundred people in a suburb of the capital, Minsk, that the authorities would try to provoke trouble among protestors.
Alexander Milinkevich is seen as the strongest of three challengers
The BBC's Emma Simpson notes that the meeting could not have been more low-key, and as ever, the event took place under the watchful eye of stony-faced plain clothes police officers.
Mr Milinkevich told the crowd he was not planning a revolution and he accused the authorities of blatant election propaganda.
"I had expected the campaign to be unfair and dishonest but I had not expected it to be so outrageous," he said.
"We want to tell the truth about it. I invite you to come to the square."
At one point, he brandished what he said was a fake campaign leaflet issued in his name.
Mr Lukashenko would, he said, win a landslide but "half of Belarus" would be laughing at the result.
The opposition is focussing its efforts now on persuading people to stage a peaceful demonstration on Sunday, our correspondent says.
"We will come out with flowers, we will come out peacefully, without any violence," Mr Milinkevich said.
Alexander Kozulin, another opposition candidate, told a rally in Minsk on Friday that it was "time for Belarus to awaken and shake off its fascist dictatorship".
He stressed, however, that protests should be non-violent.
'No conflicts here'
In a final televised election address on Friday, President Lukashenko warned foreign monitors not to "exceed their remit".
Alexander Lukashenko dominated the media during the campaign
"Observe, draw conclusions, but do not decide for us... what path the Belarusian people should take," he said.
Mr Lukashenko defended his record in office, saying the economy was strong and the republic had avoided "social, political, racial and religious conflicts".
Arguing that the presence of four rival candidates was proof of democracy, he warned that political violence would not be tolerated.
"I guarantee that there won't be a coup d'etat in this country," he said.
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.