Three migrants, including an Iraqi man, were found dead close to Poland's border with Belarus.
Poland is sending 500 additional troops to the border with Belarus in order to strengthen it against increasing migrant pressure that Warsaw says is orchestrated by Belarus and Russia to destabilise the European Union.
"We are dealing with a well-organised action directed from Minsk and Moscow," Prime Minister Mateusz Morawiecki told a news conference.
"We will defend Poland's border with full determination," Morawiecki stated after a meeting with the interior minister and the head of the Border Guards.
It comes after three migrants, including an Iraqi man, were found dead on Sunday close to the Belarusian border. They had died of hypothermia and exhaustion. Polish border guards were also able to see the body of a woman close to the border, on the Belarus side, according to Border Guards chief, General Tomasz Praga.
EU members Poland and Lithuania, which are part of the bloc’s eastern border, are facing increasing migrant pressures on their borders with Belarus. They say it is a "hybrid attack" by Belarusian President Alexander Lukashenko's regime in Minsk that is aimed at destabilising the 27-nation EU.
Morawiecki said migrants from the Middle East and Africa are paying big money in Belarus, some $2,500, for an "illusion" of a transfer to Germany, but then are left by Belarusian servicemen in the forests or bogs on the border with Poland.
They said Belarus has introduced visa-free travel with some Middle East countries that have "migration potential" to bring in migrants and push them toward Poland and Lithuania.
Poland and Lithuania are building razor-wire fences, have increased border patrols and have introduced a temporary state of emergency along their borders to stop illegal migration.
Authorities said there were over 8,000 attempts at illegal crossing from Belarus this year, including over 3,800 attempts so far in September.