The head of Belarus' security service has repeated accusations that the opposition plans to use Sunday's election to seize power by force.
Stepan Sukhorenko said the opposition was preparing violent protests to contest the results, and was smuggling supporters into the capital, Minsk.
He warned that the police would treat any protests as acts of terrorism.
Opposition candidate Alexander Milinkevich denied the accusations, and said the election would be rigged.
The EU's external affairs commissioner, Benita Ferrero-Waldner, warned on Thursday that the EU could extend a travel ban on Belarussian officials "if the elections are not conducted in a democratic manner".
She said a wave of arrests of opposition figures in the run-up to the poll was "completely unacceptable", and condemned restrictions on international election observers.
Mr Sukhorenko told a news conference on Thursday: "We are obliged to announce that under cover of elections, a violent attempt to seize power is being planned in the country.
"The actions of those who take the risk of going into the streets to attempt to destabilise the situation will be viewed as terrorism.
"Brigades of volunteers are being formed in neighbouring states. The key moment will be the detonation of several explosions," he added.
Mr Sukhorenko's comments repeated similar remarks earlier this month. President Alexander Lukashenko has also said that he will not hesitate to use force to quell protests.
Mr Lukashenko, who has been in power for more than a decade, is widely expected to win the election.
Opposition activists say he has become increasingly authoritarian, while the United States has condemned him as "Europe's last dictator".
The UN's special investigator on human rights, Adrian Severin, has condemned the government for attacking the independent media, opposition parties and rights advocates.
The authorities should "immediately cease all actions aimed at intimidating opponents, journalists and human rights defenders and jeopardising the free and fair running of the electoral campaign," he said in a statement.