Polish Prime Minister Mateusz Morawiecki said Wagner troops are poised to infiltrate NATO territory.
Over 100 mercenaries have gathered near Poland's border with Belarus, he said on Saturday.
Morawiecki warned that the fighters could pose as migrants or border guards to try and sneak in.
The Russian fighters are near Grodno, a Belarusian city 10 miles from the Polish border, Morawiecki said at a press conference in Gliwice.
Polish officials have for years accused Belarus of attempting to overwhelm Poland's border forces by sending migrants west — a charge Minsk has denied.
Persons:
Mateusz Morawiecki, Wagner, Morawiecki, Arnoldas Abramavičius, Yevgeny Prigozhin, Alexander Lukashenko, Prigozhin, Jarosław Kaczyński
Organizations:
Polish, Service, European Union, BBC, Kremlin, Poland, Agence France Presse
Locations:
Poland's, Belarus, Wall, Silicon, Grodno, Belarusian, Polish, Gliwice, Minsk, Lithuanian, Poland, Lithuania, Ukraine, Moscow