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The campaign manager for the leading opposition candidate in Belarus has been arrested on the eve of the presidential election, her office said.
A spokeswoman for candidate Svetlana Tikhanovskaya said Maria Moroz was expected to be held until Monday.
The government did not comment on the case, and it was not immediately clear on what grounds it was being held.
Alexander Lukashenko is seeking a sixth term in office on Sunday. Large opposition balls were held.
The run-up to the election has seen the rise of 37-year-old Ms Tikhanovskaya and the biggest opposition protests in a decade.
A spokeswoman for Ms Tikhanovskaya said earlier that Ms Moroz was detained on Thursday shortly after visiting the Lithuanian embassy in Minsk. The Interior Ministry denied that she had been arrested, told AFP that the campaign manager was “invited for an interview”.
Ms Moroz later said she was warned by police not to organize riots.
Stay-at-home mom Ms Tikhanovskaya is a political novice who only entered as a presidential candidate when her husband was arrested and blocked from registering.
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A second serious rival to Mr Lukashenko has also been jailed and a third has fled the country.
President Lukashenko, called by some “the last dictator of Europe”, was first elected in 1994.
