Poland has claimed Belarus and its ally Russia are behind a recent surge in migrants from the former Soviet state into the European Union.
The number of attempted illegal border crossings from Belarus into Poland has shot up in recent months from only a handful to almost 400 a day, Polish officials say.
Poland's border guards have also described increasingly aggressive behaviour by some migrants on the Belarusian side of the border, posting online videos of some throwing rocks, logs and even burning wood at Polish troops.
There have been cases of soldiers and guards ending up in hospital, and some have needed stitches after being stabbed or cut by knife-wielding assailants.
Last Tuesday, near the village of Dubicze Cerkiewne, officials said a migrant reached between the bars of the 16-foot-high barrier and stabbed a soldier in the ribs.
The government in Warsaw sees the new push at the border as an orchestrated attempt by Russia and Belarus to fuel anti-migrant sentiment, which could in turn boost far-right parties in the EU parliamentary vote.
"We are not dealing with [just] any asylum seekers here, we are dealing with a coordinated, very efficient - on many levels - operation to break the Polish border and attempts to destabilise the country," Donald Tusk, the Polish prime minister, said last week while visiting troops at the border.