Lithuania, Latvia, and Estonia will announce travel sanctions on about 30 Belarus officials, including President Alexander Lukashenko, later on, Monday, Lithuanian president Gitanas Nauseda told reporters.
The list is the first step and could be expanded later, he added.
Earlier, Lithuania said it intends to sanction the Belarus officials it holds responsible for election violations and violence against protesters.
Tens of thousands of protesters have taken to the Belarusian capital in the third weekend of demonstrations, demanding President Lukashenko's resignation.
Demonstrations began after the autocratic leader claimed victory in an election on August 9, which opponents say was rigged.
Police said 125 people arrested in Sunday's rally, but Ales Bilyatsky of the Viasna human rights organization said more than 200 detained.
The marchers, chanting "Freedom!" and "Resign!" eventually reached the outskirts of the presidential palace, which was blocked off by shield-bearing riot police.
Demonstrators were seen carrying the old Belarusian red and white flags.