The Belarus authorities have jailed about 600 demonstrators for up to two weeks in a crackdown on protests against the re-election of President Alexander Lukashenko.
Some detainees may face longer terms – as much as 15 years – if found guilty of taking part in “mass disturbances”.
At least seven presidential candidates were among those detained. Some of them were reportedly also beaten by police.
Observers called the poll “flawed” and the US and EU condemned the crackdown.
The Russian Union of Journalists has demanded the immediate release of journalists arrested while covering the protests in the capital Minsk. They have urged the Kremlin to put pressure on Belarus to free their colleagues.