Early voting has already started in Belarus
A delegation of European Union MPs has abandoned plans to go to Belarus to monitor the presidential election after its members were refused visas.
The head of the European delegation told the BBC he feared the Belarussian government would use force to suppress popular protests.
A group of monitors from the European security organisation, the OSCE, has also been refused entry.
President Alexander Lukashenko is seeking a third term in office.
Tuesday was the first day of early voting in a presidential election officially set for Sunday.
Opposition groups say early voting is an opportunity for the president to rig the poll.
The BBC's Alix Kroeger, in Strasbourg, said the MEPs who were supposed to be monitoring the elections in Belarus now say they see no chance of a democratic vote.
It was surreal, we were afraid but we stuck together and we are young
Michael Johnson, DSU
Eyewitness: Expelled from Belarus
The head of the delegation, Polish MEP Bogdan Klich, said they were told any attempt to enter Belarus would be treated as a provocation and would be blocked at the border.
The delegation now plans to monitor the elections from Brussels and Warsaw. Mr Klich said the MEPs would not urge the people of Belarus to take to the streets.
He said it was up to Belarussian civil society to decide how to react.
Human rights groups have long complained about oppression of opposition members in Belarus.
On Wednesday, a senior aide to the main opposition candidate, Alexander Milinkevich, said he had been arrested for a second time in the run-up to the vote.
Anatoly Lebedko said police stopped a car in which he was travelling and detained him.
It is the latest in a series of arrests of aides and supporters of Mr Milinkevich, who correspondents say is the main challenger to President Lukashenko in next week's elections.
On Tuesday, eight members of a team of unofficial election observers from Denmark and Sweden were ordered to leave Belarus.
Bjorn Senstrom, from Sweden, told the BBC's Europe Today that he and his colleague had been banned from re-entering Belarus.
"We have been charged with doing illegal activity during campaigning for foreigners," he said.
"We're not allowed to enter the country [for] two years."