Polish security forces were seen firing water cannon at migrants stranded on the Belarus side of the border, in video broadcast by Belarusian state media and released by the Polish Defence Ministry on Tuesday.
The footage showed jets of water dousing the migrants at the Kuznica-Bruzgi crossing, one of the main locations where people have been amassing as they attempt to illegally enter EU member Poland.
The Defence Ministry in Warsaw said the border forces had responded to an "attack" by migrants.
The ministry said the asylum seekers had pelted officers with rocks and other objects, and that Belarus had equipped the migrants with stun grenades.
According to unconfirmed reports, the Polish side also used tear gas.
Border tensions that had been simmering since this summer dramatically escalated this month as more and more migrants - most from war-torn countries like Iraq and Afghanistan - gathered at the European Union's eastern frontier.
In freezing conditions
The EU accuses Belarusian strongman Alexander Lukashenko of luring these desperate people to Belarus and then sending them to the border with Poland, where they have been camped out in freezing conditions with little food and shelter.
Brussels says the migrants are being used as pawns, part of an attempt to put pressure on the EU for refusing to recognize Lukashenko's re-election last year and imposing several rounds of wide-ranging sanctions for the violent repression of protesters.