"Russia and Belarus are intensifying pressure on the border, increasing the number of provocations, and we must be aware that this number will increase," Polish Prime Minister Mateusz Morawiecki said.

"Today, Polish borders and the border of Lithuania are the borders of the free world, taming the despotism from the east," he added, as he hosted Lithuanian President Gitanas Nauseda in Suwalki, in the northeast of the country.

Morawiecki also said that Warsaw had information about "some 4,000 Wagner fighters" currently based in the Belarusian territory.

Polish Minister of Defence Mariusz Blaszczak said more military helicopters had been deployed to reinforce the country's eastern border with Belarus.

"If it's justified, the soldiers will use their weapons," Blaszczak added.

On Tuesday, two Belarusian helicopters violated Polish airspace at low altitude, their presence registered and shared in social media by the inhabitants of the border area.

Poland's army initially denied the violation took place, before confirming it in a statement issued later the same day.

Their initial response drew criticism from the opposition and triggered calls for the resignation of the defence minister.

NATO member Poland is on the alliance's eastern flank.