The leaders of Latvia, Lithuania and Estonia have called on Belarus to hold "free and fair" elections following its disputed presidential vote.
In a joint statement, the three prime ministers called for a new election to be held with the involvement of international observers.
Mass protests erupted after President Alexander Lukashenko claimed a landslide victory in the 9 August vote.
The result has been condemned with widespread allegations of vote-rigging.
On Friday, European Union foreign ministers held an emergency meeting and agreed to prepare new sanctions on Belarusian officials responsible "for violence and falsification". The US has also condemned the election as "not free and fair".
The Central Election Commission says Mr Lukashenko won 80.1% of the vote and the main opposition candidate Svetlana Tikhanovskaya 10.12%.
But Ms Tikhanovskaya insists that where votes were properly counted, she won support ranging from 60% to 70%.
Protests against President Lukashenko are expected to continue over the weekend, after Ms Tikhanovskaya called on mayors to organise "peaceful mass gatherings" on Saturday and Sunday.
What did the Baltic leaders say?
In a joint statement on Saturday, the prime ministers of the three Baltic republics – Latvia, Lithuania and Estonia – "expressed deep concern at the violent crackdown… and the political repression of the opposition by the authorities".
The leaders said the presidential election was "neither free nor fair" and called for a "transparent" vote "with the participation of international observers".
"The prime ministers urge the Belarusian authorities to refrain from violence against peaceful demonstrators [and to] release all political prisoners and those that have been detained," the statement added.
Ms Tikhanovskaya fled to Lithuania following the election after she publicly denounced the results. She said he had sent her children to Lithuania for safety before the vote.
Lithuania and Latvia have also previously said they are prepared to mediate in Belarus, provided the authorities stopped violence against protesters and formed a national council with members of civil society. They warned that the alternative was sanctions.
What's the latest with the protests?
On Saturday, opposition supporters gathered for the funeral of a man who died during last week's demonstrations in the capital, Minsk. Crowds waved flags, lit candles and laid flowers at the scene.
A "March for Freedom" is planned in the centre of the city on Sunday, a week after the disputed election.
It follows Ms Tikhanovskaya's call for further peaceful rallies across the country on Friday. "Don't stay on the sidelines," she said.