Countries near Belarus are warning that the migrant crisis on the European Union's eastern borders could escalate into a military confrontation.
Video released by the Polish defense ministry is said to show Belarus border guards carrying heavy arms at the border, including grenade launchers and sniper rifles.
Reuters couldn't verify the grenade launcher claim, but it comes as Latvia, Estonia, and Lithuania -- which are both EU and NATO members -- say the incident is posing a serious threat to European security.
And Ukraine, which is not an EU member, but is wary of becoming another flashpoint, says it will deploy 8,500 more troops to reinforce its own frontier.
Belarus President Alexander Lukashenko is threatening to retaliate by shutting down the transit of Russian natural gas to the rest of Europe via Belarus.
But Moscow reacted angrily in the past when Ukraine, another transit country, disrupted supplies of gas to the West.
Belarus opponents allege that Minsk is using migrants to retaliate for EU sanctions.
Large groups of migrants started flying to the country's capital Minsk this spring with the help of Belarusian travel agencies.
They then head to the border and try to cross into the EU, sometimes with wire cutters they say were given to them by Belarusian border guards.
Now, trapped between two borders, the migrants have endured freezing weather in makeshift camps.
Video footage showed children holding up signs saying "sorry."
Poland has reported at least seven migrant deaths in the months-long crisis.