The ministry said in an August 19 statement that Belarusian authorities detained the three on August 18, a day before a meeting of the Union of Poles in Belarus (SPB).
Last year, Minsk accused the SPB of fomenting a revolution among Belarusian Poles.
Warsaw intervened in the dispute. Relations between Warsaw and Minsk soured when Belarusian President Alyaksandr Lukashenka accused Poland of interfering in Belarus's internal affairs.
The dispute led to a series of tit-for-tat expulsions of diplomats from both countries.
(AFP)