The reported move came amid a mounting campaign by officials to pressure the opposition ahead of the presidential election on March 19.
Iosif Syaredzich, publisher of the "Narodnaya volya" newspaper, said two trucks carrying 250,000 copies were seized at the border late on March 5.
He said the paper had printed a special edition with photographs showing last week's beating of an opposition candidate, activists, and reporters by security agents.
"Narodnaya volya," whose print run is normally around 30,000, is printed in Russia to avoid being shut down by Belarusian authorities.
Authorities have accused the newspaper of unlawful campaigning.
Belarus' authoritarian President Alyaksandr Lukashenka is seeking a third term in the March 19 election.
(AP)