The Belarus government has ordered eight members of a Scandinavian team of unofficial election observers to leave.
Foreigners will monitor the election - but critics say it will not be fair
The two Swedes and six Danes were part of a monitoring team sent by the unaccredited Danish group Silba.
They were arrested on Tuesday - the first day of early voting ahead of a presidential election officially set for Sunday.
Opposition groups say early voting is an opportunity for the president, Alexander Lukashenko, to rig the poll.
The Swedes, Thomas Ochman and Bjorn Stenstrom - members of Sweden's Liberal Party - were arrested in the western city of Grodno after visiting a polling station there.
They are accused of breaking a law which states that conducting opinion polls is banned in Belarus.
Six other representatives from the Friends Across Borders NGO, which includes members of Silba and the Social Democratic Youth of Denmark (DSU) were arrested in Minsk.
Michael Johnson, the DSU co-ordinator for Belarus, said the police confiscated computer equipment and questioned them for four hours at a police station.
He said he was afraid the arrests showed how Mr Lukashenko's "repressive dictatorship" could crack down on opposition members after the elections.
The Scandinavian team is not part of the official election monitoring mission of the Organisation for Security and Co-operation in Europe, which has been invited by Belarus to cover the vote.