His words came after Polish lawmakers last Thursday backed a government plan to build a wall on the Belarus border, in a bid to stave off an influx of migrants from the Middle East.
Speaking in an interview with the Sieci weekly, published on Monday, Kaczyński said: "We will defend the Polish border. That's why we are building the security barrier."
He added that the decision to build the barrier had been made in response to the policies of eastern neighbour Belarus, which was sending thousands of illegal migrants towards the Polish border.
“No one in their right mind can fail to notice that it is in fact a form of aggression, a form of hybrid war, and we are entitled to defend ourselves,” Kaczyński said, as quoted by state news agency PAP.
'We are defending EU border'
He warned that “the crisis will otherwise escalate, with further thousands of migrants sent to our frontier.”
He added: "We are also defending the external border of the European Union."
Kaczyński said in the interview that Belarus's strongman leader Alexander Lukashenko “is seeking to make us and the EU acquiesce, recognise his authority, stop supporting those Belarusians who are fighting for freedom."
“Both he and Russian President Vladimir Putin, who is backing him, are deadly scared of what they call colour revolutions,” Kaczyński was quoted as saying.
He also argued that the migrant crisis “could be part of a wider offensive against the West, similar to what was done to Ukraine,” and so “those who have designs on Poland must know they won’t have it easy with us.”
Kaczyński said in the interview Poland was “taking into account various scenarios and stepping up its security in every possible way.”
“And so we will soon present a plan to give a major boost to the Polish armed forces,” he announced.
The spokesman for Poland's security-services chief last week said there was hard evidence of Russian involvement in the migrant crisis on the Polish-Belarusian border.